<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:3ade1e9c-8754-4bce-84b9-83231d17b989,g:c324a16d-aca9-45c2-8b50-8666bee7377b-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.abivax.com/role/Coverpage" xlink:type="simple" xlink:href="abvx-20251231.xsd#Coverpage"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/Coverpage" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_3683f404-bf42-4fab-9fdf-9658d3fcae93" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntitiesTable_3683f404-bf42-4fab-9fdf-9658d3fcae93" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityListingsExchangeAxis_9b371dcd-3173-44c8-96ae-407bfda4e9c7" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityListingsExchangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_3683f404-bf42-4fab-9fdf-9658d3fcae93" xlink:to="loc_dei_EntityListingsExchangeAxis_9b371dcd-3173-44c8-96ae-407bfda4e9c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_ExchangeDomain_9b371dcd-3173-44c8-96ae-407bfda4e9c7_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_ExchangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_EntityListingsExchangeAxis_9b371dcd-3173-44c8-96ae-407bfda4e9c7" xlink:to="loc_dei_ExchangeDomain_9b371dcd-3173-44c8-96ae-407bfda4e9c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_ExchangeDomain_d6773f1b-50d0-4911-886b-d40ecbca0f02" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_ExchangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_EntityListingsExchangeAxis_9b371dcd-3173-44c8-96ae-407bfda4e9c7" xlink:to="loc_dei_ExchangeDomain_d6773f1b-50d0-4911-886b-d40ecbca0f02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AmericanDepositorySharesNASDAQGlobalMarketMember_7705cdaa-90b8-4635-9a6d-85127451d266" xlink:href="abvx-20251231.xsd#abvx_AmericanDepositorySharesNASDAQGlobalMarketMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_ExchangeDomain_d6773f1b-50d0-4911-886b-d40ecbca0f02" xlink:to="loc_abvx_AmericanDepositorySharesNASDAQGlobalMarketMember_7705cdaa-90b8-4635-9a6d-85127451d266" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OrdinarySharesNASDAQGlobalMarketMember_58096e37-81b7-4e7d-8a3a-a80fdf46b1ec" xlink:href="abvx-20251231.xsd#abvx_OrdinarySharesNASDAQGlobalMarketMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_ExchangeDomain_d6773f1b-50d0-4911-886b-d40ecbca0f02" xlink:to="loc_abvx_OrdinarySharesNASDAQGlobalMarketMember_58096e37-81b7-4e7d-8a3a-a80fdf46b1ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressesAddressTypeAxis_3e8c3ed0-6ee8-4dfc-ba9e-c8b054c86634" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressesAddressTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_3683f404-bf42-4fab-9fdf-9658d3fcae93" xlink:to="loc_dei_EntityAddressesAddressTypeAxis_3e8c3ed0-6ee8-4dfc-ba9e-c8b054c86634" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AddressTypeDomain_3e8c3ed0-6ee8-4dfc-ba9e-c8b054c86634_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AddressTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_EntityAddressesAddressTypeAxis_3e8c3ed0-6ee8-4dfc-ba9e-c8b054c86634" xlink:to="loc_dei_AddressTypeDomain_3e8c3ed0-6ee8-4dfc-ba9e-c8b054c86634_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AddressTypeDomain_3d4c9cbc-bbd3-4033-ba6f-032913516eb3" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AddressTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_EntityAddressesAddressTypeAxis_3e8c3ed0-6ee8-4dfc-ba9e-c8b054c86634" xlink:to="loc_dei_AddressTypeDomain_3d4c9cbc-bbd3-4033-ba6f-032913516eb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_BusinessContactMember_289dbd96-b92a-4337-9685-e37de3cf7b1a" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_BusinessContactMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_AddressTypeDomain_3d4c9cbc-bbd3-4033-ba6f-032913516eb3" xlink:to="loc_dei_BusinessContactMember_289dbd96-b92a-4337-9685-e37de3cf7b1a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_9e9f4308-a9df-4a66-acb0-ec65b88fe5e4" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_DocumentType_9e9f4308-a9df-4a66-acb0-ec65b88fe5e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentRegistrationStatement_951bf81b-8727-4ef0-9a45-1ea5c7a4d9a9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentRegistrationStatement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_DocumentRegistrationStatement_951bf81b-8727-4ef0-9a45-1ea5c7a4d9a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentAnnualReport_42769bf8-d95e-4ae5-b044-9cf9f60ca3e5" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentAnnualReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_DocumentAnnualReport_42769bf8-d95e-4ae5-b044-9cf9f60ca3e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_8e035edb-f360-430b-ab5c-0283169c52f9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_DocumentPeriodEndDate_8e035edb-f360-430b-ab5c-0283169c52f9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_fc021916-1a5e-446e-aba3-c5d1fdb05ce5" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_CurrentFiscalYearEndDate_fc021916-1a5e-446e-aba3-c5d1fdb05ce5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_a067fac4-2f93-4865-9704-c4dd7141580b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_DocumentTransitionReport_a067fac4-2f93-4865-9704-c4dd7141580b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentShellCompanyReport_94fb1c4b-89fc-47cc-b597-d0b5008c9ce1" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentShellCompanyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_DocumentShellCompanyReport_94fb1c4b-89fc-47cc-b597-d0b5008c9ce1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_193ff3d9-ef6e-4ed7-9d8b-35e07410a58e" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityFileNumber_193ff3d9-ef6e-4ed7-9d8b-35e07410a58e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_4bf0fbf9-2aaf-49cc-867e-84da6c96e7d8" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityRegistrantName_4bf0fbf9-2aaf-49cc-867e-84da6c96e7d8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_b66571b1-9926-49f9-ab37-d353dc23666b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityIncorporationStateCountryCode_b66571b1-9926-49f9-ab37-d353dc23666b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_ContactPersonnelName_3aa9dd95-0708-4b18-95b8-0dada626724d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_ContactPersonnelName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_ContactPersonnelName_3aa9dd95-0708-4b18-95b8-0dada626724d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_1775d9c6-40e9-46a2-85d4-19f98b52c482" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityAddressAddressLine1_1775d9c6-40e9-46a2-85d4-19f98b52c482" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_eec7737a-a827-4685-bd53-2fbe1bfef887" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityAddressPostalZipCode_eec7737a-a827-4685-bd53-2fbe1bfef887" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_293d4492-a60e-4a0c-8081-ecdb6d4ef31d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityAddressCityOrTown_293d4492-a60e-4a0c-8081-ecdb6d4ef31d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCountry_ce4ac6f5-3f1e-421a-99d8-29ea9962f6ef" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressCountry"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityAddressCountry_ce4ac6f5-3f1e-421a-99d8-29ea9962f6ef" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_70a392c5-9d0f-41ef-9f22-cb59f9e64d85" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_CityAreaCode_70a392c5-9d0f-41ef-9f22-cb59f9e64d85" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_03349789-3959-4262-a8cd-eb8cf6d5b998" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_LocalPhoneNumber_03349789-3959-4262-a8cd-eb8cf6d5b998" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_14b72046-ef28-4cb3-aa79-e66f9b5ef6e0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_Security12bTitle_14b72046-ef28-4cb3-aa79-e66f9b5ef6e0" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_2d42f606-70ad-493f-87f9-85a8ca69486a" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_TradingSymbol_2d42f606-70ad-493f-87f9-85a8ca69486a" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_f7b9b7e1-62ac-4d40-a4de-68903994ff4d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_SecurityExchangeName_f7b9b7e1-62ac-4d40-a4de-68903994ff4d" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_8df04137-de20-4774-8c71-a9ac1ef47c5b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_8df04137-de20-4774-8c71-a9ac1ef47c5b" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityWellKnownSeasonedIssuer_c9c528ae-379c-418e-b180-0a842a803974" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityWellKnownSeasonedIssuer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityWellKnownSeasonedIssuer_c9c528ae-379c-418e-b180-0a842a803974" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityVoluntaryFilers_df28ca70-4a7a-4592-bf32-8e0b5f9a22b4" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityVoluntaryFilers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityVoluntaryFilers_df28ca70-4a7a-4592-bf32-8e0b5f9a22b4" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_20ed84de-ec19-4ebb-b3d5-832b4ac0335d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityCurrentReportingStatus_20ed84de-ec19-4ebb-b3d5-832b4ac0335d" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_7ad61ce1-64e0-49dc-b440-eb0c2f2d4053" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityInteractiveDataCurrent_7ad61ce1-64e0-49dc-b440-eb0c2f2d4053" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_a2d496dc-c791-436d-b318-e8b9e16a7f93" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityFilerCategory_a2d496dc-c791-436d-b318-e8b9e16a7f93" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_88c612ec-0aa7-4674-8ae8-166139320459" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityEmergingGrowthCompany_88c612ec-0aa7-4674-8ae8-166139320459" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityExTransitionPeriod_303b20f8-9689-4277-a36b-d70ab5a50cc1" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityExTransitionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityExTransitionPeriod_303b20f8-9689-4277-a36b-d70ab5a50cc1" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_IcfrAuditorAttestationFlag_1de8821d-dd2a-479f-b6e4-03daf5b1ab15" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_IcfrAuditorAttestationFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_IcfrAuditorAttestationFlag_1de8821d-dd2a-479f-b6e4-03daf5b1ab15" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFinStmtErrorCorrectionFlag_76008dc1-bf36-4866-aa77-5e3b982c4bc0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentFinStmtErrorCorrectionFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_DocumentFinStmtErrorCorrectionFlag_76008dc1-bf36-4866-aa77-5e3b982c4bc0" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentAccountingStandard_04b2dc15-df35-4df4-b87b-fefd28ab63c9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentAccountingStandard"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_DocumentAccountingStandard_04b2dc15-df35-4df4-b87b-fefd28ab63c9" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_3a4ba0d0-1ec6-439f-b462-0a0ace98522d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityShellCompany_3a4ba0d0-1ec6-439f-b462-0a0ace98522d" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_3d340220-a749-486d-aec9-362c05614707" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_AmendmentFlag_3d340220-a749-486d-aec9-362c05614707" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_31e4af00-e5c6-4647-b79c-59ff991bbd6b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_DocumentFiscalYearFocus_31e4af00-e5c6-4647-b79c-59ff991bbd6b" xlink:type="arc" order="33"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_e2de3586-98c9-4ef6-8a17-a152b0405207" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_DocumentFiscalPeriodFocus_e2de3586-98c9-4ef6-8a17-a152b0405207" xlink:type="arc" order="34"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_a615e093-6886-4a48-93b5-755e6a409a14" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_EntityCentralIndexKey_a615e093-6886-4a48-93b5-755e6a409a14" xlink:type="arc" order="35"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_NoTradingSymbolFlag_10924dd2-5460-4fb4-a2aa-5321f0a365c2" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_NoTradingSymbolFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_576d111d-9ba0-4fab-bb6c-dfd7141fd6d4" xlink:to="loc_dei_NoTradingSymbolFlag_10924dd2-5460-4fb4-a2aa-5321f0a365c2" xlink:type="arc" order="36"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSHAREHOLDERSEQUITY" xlink:type="simple" xlink:href="abvx-20251231.xsd#CONSOLIDATEDSTATEMENTSOFCHANGESINSHAREHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSHAREHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_StatementOfChangesInEquityLineItems_023018de-2d00-40f0-9b6f-3a54ea3e380e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_StatementOfChangesInEquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_StatementOfChangesInEquityTable_d00a493c-cb99-445c-837a-1e3427d39b07" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_StatementOfChangesInEquityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_StatementOfChangesInEquityLineItems_023018de-2d00-40f0-9b6f-3a54ea3e380e" xlink:to="loc_ifrs-full_StatementOfChangesInEquityTable_d00a493c-cb99-445c-837a-1e3427d39b07" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ComponentsOfEquityAxis_e3ea0d07-2c87-4e1a-a8e6-0481a8872c8b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_StatementOfChangesInEquityTable_d00a493c-cb99-445c-837a-1e3427d39b07" xlink:to="loc_ifrs-full_ComponentsOfEquityAxis_e3ea0d07-2c87-4e1a-a8e6-0481a8872c8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ComponentsOfEquityDomain_e3ea0d07-2c87-4e1a-a8e6-0481a8872c8b_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ComponentsOfEquityAxis_e3ea0d07-2c87-4e1a-a8e6-0481a8872c8b" xlink:to="loc_ifrs-full_ComponentsOfEquityDomain_e3ea0d07-2c87-4e1a-a8e6-0481a8872c8b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ComponentsOfEquityDomain_d67da622-71de-4eef-8b04-f38112f010fa" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ComponentsOfEquityAxis_e3ea0d07-2c87-4e1a-a8e6-0481a8872c8b" xlink:to="loc_ifrs-full_ComponentsOfEquityDomain_d67da622-71de-4eef-8b04-f38112f010fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IssuedCapitalMember_cac0207c-84fc-431e-9190-61d7dc6043f3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IssuedCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ComponentsOfEquityDomain_d67da622-71de-4eef-8b04-f38112f010fa" xlink:to="loc_ifrs-full_IssuedCapitalMember_cac0207c-84fc-431e-9190-61d7dc6043f3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_SharePremiumMember_854d164e-1809-4d61-96ce-da34d3f037ac" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SharePremiumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ComponentsOfEquityDomain_d67da622-71de-4eef-8b04-f38112f010fa" xlink:to="loc_ifrs-full_SharePremiumMember_854d164e-1809-4d61-96ce-da34d3f037ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ReserveOfExchangeDifferencesOnTranslationMember_6fe9dda0-afec-4e5a-bed8-e6c07383d136" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ReserveOfExchangeDifferencesOnTranslationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ComponentsOfEquityDomain_d67da622-71de-4eef-8b04-f38112f010fa" xlink:to="loc_ifrs-full_ReserveOfExchangeDifferencesOnTranslationMember_6fe9dda0-afec-4e5a-bed8-e6c07383d136" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RetainedEarningsExcludingProfitLossForReportingPeriodMember_e069f920-2e19-425a-8156-69a5ac442516" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RetainedEarningsExcludingProfitLossForReportingPeriodMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ComponentsOfEquityDomain_d67da622-71de-4eef-8b04-f38112f010fa" xlink:to="loc_ifrs-full_RetainedEarningsExcludingProfitLossForReportingPeriodMember_e069f920-2e19-425a-8156-69a5ac442516" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RetainedEarningsProfitLossForReportingPeriodMember_5c185867-b2a4-4f23-9448-28e5382d9b2b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RetainedEarningsProfitLossForReportingPeriodMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ComponentsOfEquityDomain_d67da622-71de-4eef-8b04-f38112f010fa" xlink:to="loc_ifrs-full_RetainedEarningsProfitLossForReportingPeriodMember_5c185867-b2a4-4f23-9448-28e5382d9b2b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialAgreementAxis_96504be2-b918-46f6-8638-0b4ccc2274e6" xlink:href="abvx-20251231.xsd#abvx_FinancialAgreementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_StatementOfChangesInEquityTable_d00a493c-cb99-445c-837a-1e3427d39b07" xlink:to="loc_abvx_FinancialAgreementAxis_96504be2-b918-46f6-8638-0b4ccc2274e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialAgreementDomain_96504be2-b918-46f6-8638-0b4ccc2274e6_default" xlink:href="abvx-20251231.xsd#abvx_FinancialAgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_FinancialAgreementAxis_96504be2-b918-46f6-8638-0b4ccc2274e6" xlink:to="loc_abvx_FinancialAgreementDomain_96504be2-b918-46f6-8638-0b4ccc2274e6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialAgreementDomain_d84c840d-b88b-40cb-9dab-07cce24bc517" xlink:href="abvx-20251231.xsd#abvx_FinancialAgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_FinancialAgreementAxis_96504be2-b918-46f6-8638-0b4ccc2274e6" xlink:to="loc_abvx_FinancialAgreementDomain_d84c840d-b88b-40cb-9dab-07cce24bc517" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos1Member_019cc2f3-bb23-77de-a9e7-25c4c1873464" xlink:href="abvx-20251231.xsd#abvx_Kreos1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FinancialAgreementDomain_d84c840d-b88b-40cb-9dab-07cce24bc517" xlink:to="loc_abvx_Kreos1Member_019cc2f3-bb23-77de-a9e7-25c4c1873464" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingMember_019c4326-72ec-77dc-8079-3eeb481efbff" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FinancialAgreementDomain_d84c840d-b88b-40cb-9dab-07cce24bc517" xlink:to="loc_abvx_KreosClaretFinancingMember_019c4326-72ec-77dc-8079-3eeb481efbff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherEquityAgreementsMember_019cc2f3-fb30-7c47-8500-ae95d7ff5f1c" xlink:href="abvx-20251231.xsd#abvx_OtherEquityAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FinancialAgreementDomain_d84c840d-b88b-40cb-9dab-07cce24bc517" xlink:to="loc_abvx_OtherEquityAgreementsMember_019cc2f3-fb30-7c47-8500-ae95d7ff5f1c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialInstrumentsAxis_019c4327-ff74-7493-8d9c-ce605a7ab130" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialInstrumentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_StatementOfChangesInEquityTable_d00a493c-cb99-445c-837a-1e3427d39b07" xlink:to="loc_ifrs-full_ClassesOfFinancialInstrumentsAxis_019c4327-ff74-7493-8d9c-ce605a7ab130" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialInstrumentsDomain_019c4327-ff74-7493-8d9c-ce605a7ab130_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialInstrumentsAxis_019c4327-ff74-7493-8d9c-ce605a7ab130" xlink:to="loc_ifrs-full_ClassesOfFinancialInstrumentsDomain_019c4327-ff74-7493-8d9c-ce605a7ab130_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialInstrumentsDomain_019c4327-ff74-7050-bb5e-55a56c78fc5a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialInstrumentsAxis_019c4327-ff74-7493-8d9c-ce605a7ab130" xlink:to="loc_ifrs-full_ClassesOfFinancialInstrumentsDomain_019c4327-ff74-7050-bb5e-55a56c78fc5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosOCABSAMember_019c4328-2d72-7643-a937-e304693e0682" xlink:href="abvx-20251231.xsd#abvx_KreosOCABSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialInstrumentsDomain_019c4327-ff74-7050-bb5e-55a56c78fc5a" xlink:to="loc_abvx_KreosOCABSAMember_019c4328-2d72-7643-a937-e304693e0682" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_019c4328-803a-7fe7-9447-f522113dc268" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_StatementOfChangesInEquityTable_d00a493c-cb99-445c-837a-1e3427d39b07" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_019c4328-803a-7fe7-9447-f522113dc268" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019c4328-803a-7fe7-9447-f522113dc268_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019c4328-803a-7fe7-9447-f522113dc268" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019c4328-803a-7fe7-9447-f522113dc268_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019c4328-803a-76b9-ba47-f702bd6206c9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019c4328-803a-7fe7-9447-f522113dc268" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019c4328-803a-76b9-ba47-f702bd6206c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_HeightsConvertibleNotesMember_019c4328-aa77-7ebf-9397-3ebb8d0728e3" xlink:href="abvx-20251231.xsd#abvx_HeightsConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019c4328-803a-76b9-ba47-f702bd6206c9" xlink:to="loc_abvx_HeightsConvertibleNotesMember_019c4328-aa77-7ebf-9397-3ebb8d0728e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfSharesIssued_2efdbd89-d5f1-47d6-a514-9413333ac0fb" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_StatementOfChangesInEquityLineItems_023018de-2d00-40f0-9b6f-3a54ea3e380e" xlink:to="loc_ifrs-full_NumberOfSharesIssued_2efdbd89-d5f1-47d6-a514-9413333ac0fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ReconciliationOfNumberOfSharesOutstandingAbstract_1bd1f087-6147-4445-b545-efb07cdc3259" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ReconciliationOfNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_StatementOfChangesInEquityLineItems_023018de-2d00-40f0-9b6f-3a54ea3e380e" xlink:to="loc_ifrs-full_ReconciliationOfNumberOfSharesOutstandingAbstract_1bd1f087-6147-4445-b545-efb07cdc3259" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease_997cd59e-2f4a-46ac-9480-007e5f92971d" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ReconciliationOfNumberOfSharesOutstandingAbstract_1bd1f087-6147-4445-b545-efb07cdc3259" xlink:to="loc_abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease_997cd59e-2f4a-46ac-9480-007e5f92971d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants_54aebae5-07c1-47a6-b495-034af3c1479f" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ReconciliationOfNumberOfSharesOutstandingAbstract_1bd1f087-6147-4445-b545-efb07cdc3259" xlink:to="loc_abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants_54aebae5-07c1-47a6-b495-034af3c1479f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughConversionOfConvertibleInstruments_019c4327-404a-7d2e-bb32-556bb67a5e60" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughConversionOfConvertibleInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ReconciliationOfNumberOfSharesOutstandingAbstract_1bd1f087-6147-4445-b545-efb07cdc3259" xlink:to="loc_abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughConversionOfConvertibleInstruments_019c4327-404a-7d2e-bb32-556bb67a5e60" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfFreeSharesIssued_267fb8ab-f60b-4b3a-bc7f-7ee61a6cb399" xlink:href="abvx-20251231.xsd#abvx_NumberOfFreeSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ReconciliationOfNumberOfSharesOutstandingAbstract_1bd1f087-6147-4445-b545-efb07cdc3259" xlink:to="loc_abvx_NumberOfFreeSharesIssued_267fb8ab-f60b-4b3a-bc7f-7ee61a6cb399" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfSharesIssued_704f8c32-a4c9-465d-ac4d-a009634d34d5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfSharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_Equity_d415f447-a573-4978-a1b5-9f5d1d5ad65d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Equity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_StatementOfChangesInEquityLineItems_023018de-2d00-40f0-9b6f-3a54ea3e380e" xlink:to="loc_ifrs-full_Equity_d415f447-a573-4978-a1b5-9f5d1d5ad65d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ChangesInEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_StatementOfChangesInEquityLineItems_023018de-2d00-40f0-9b6f-3a54ea3e380e" xlink:to="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProfitLoss_dea1978d-1268-462c-a19d-666c37057732" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:to="loc_ifrs-full_ProfitLoss_dea1978d-1268-462c-a19d-666c37057732" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OtherComprehensiveIncome_5950f862-1629-4df2-8620-69b7888e57e1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherComprehensiveIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:to="loc_ifrs-full_OtherComprehensiveIncome_5950f862-1629-4df2-8620-69b7888e57e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ComprehensiveIncome_4447ceaa-79c4-4340-b6b6-df4b671b1a30" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComprehensiveIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:to="loc_ifrs-full_ComprehensiveIncome_4447ceaa-79c4-4340-b6b6-df4b671b1a30" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughAppropriationOfRetainedEarnings_bd0d9050-9e02-497a-8427-368a041b8812" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughAppropriationOfRetainedEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughAppropriationOfRetainedEarnings_bd0d9050-9e02-497a-8427-368a041b8812" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IssueOfEquity_99dd4952-5d32-44f7-a127-a0991ad246ca" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IssueOfEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:to="loc_ifrs-full_IssueOfEquity_99dd4952-5d32-44f7-a127-a0991ad246ca" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ShareIssueRelatedCostCredit_3905a2b2-20c4-4021-913f-950c3ac3774f" xlink:href="abvx-20251231.xsd#abvx_ShareIssueRelatedCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:to="loc_abvx_ShareIssueRelatedCostCredit_3905a2b2-20c4-4021-913f-950c3ac3774f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IssueOfConvertibleInstruments_019cc2ef-dc2f-7479-b54d-e834b738a92a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IssueOfConvertibleInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:to="loc_ifrs-full_IssueOfConvertibleInstruments_019cc2ef-dc2f-7479-b54d-e834b738a92a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseThroughIssuanceOfWarrantsEquity_898a034e-8b3c-4a0f-9b07-6cfaf2b9f19a" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseThroughIssuanceOfWarrantsEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:to="loc_abvx_IncreaseDecreaseThroughIssuanceOfWarrantsEquity_898a034e-8b3c-4a0f-9b07-6cfaf2b9f19a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughExerciseOfWarrantsEquity_245361c1-f6e3-4a76-9218-276e2a85af41" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughExerciseOfWarrantsEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughExerciseOfWarrantsEquity_245361c1-f6e3-4a76-9218-276e2a85af41" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughConversionOfConvertibleInstruments_019c4327-849d-76ff-ad76-73d6c12b22e0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughConversionOfConvertibleInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughConversionOfConvertibleInstruments_019c4327-849d-76ff-ad76-73d6c12b22e0" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseFromFreeSharesIssued_3748677d-9c78-4973-9149-62fa6d0b2e00" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseFromFreeSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:to="loc_abvx_IncreaseDecreaseFromFreeSharesIssued_3748677d-9c78-4973-9149-62fa6d0b2e00" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughSharebasedPaymentTransactions_304ea5cb-1bb1-407a-aec6-ac0e31a8101f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughSharebasedPaymentTransactions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughSharebasedPaymentTransactions_304ea5cb-1bb1-407a-aec6-ac0e31a8101f" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughTreasuryShareTransactions_41fce087-6514-446c-918e-739a726a6ddb" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughTreasuryShareTransactions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ChangesInEquityAbstract_840ca2eb-2780-4e09-ab18-0a451c76abf0" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughTreasuryShareTransactions_41fce087-6514-446c-918e-739a726a6ddb" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_Equity_13cb43dd-3c02-4c7d-b120-06c027396258" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Equity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/BasisofpreparationDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#BasisofpreparationDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/BasisofpreparationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_3727c861-3787-40da-8ee4-8557a018979d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable_5a04552b-e148-4136-bb64-1022dc6d3aa2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_3727c861-3787-40da-8ee4-8557a018979d" xlink:to="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable_5a04552b-e148-4136-bb64-1022dc6d3aa2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SaleOfStockAxis_9636aa04-a03c-4fe6-979f-e883570254bf" xlink:href="abvx-20251231.xsd#abvx_SaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable_5a04552b-e148-4136-bb64-1022dc6d3aa2" xlink:to="loc_abvx_SaleOfStockAxis_9636aa04-a03c-4fe6-979f-e883570254bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SaleOfStockDomain_9636aa04-a03c-4fe6-979f-e883570254bf_default" xlink:href="abvx-20251231.xsd#abvx_SaleOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_SaleOfStockAxis_9636aa04-a03c-4fe6-979f-e883570254bf" xlink:to="loc_abvx_SaleOfStockDomain_9636aa04-a03c-4fe6-979f-e883570254bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SaleOfStockDomain_af5a6cb4-a79d-443d-8a0d-0af5895ce4ae" xlink:href="abvx-20251231.xsd#abvx_SaleOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_SaleOfStockAxis_9636aa04-a03c-4fe6-979f-e883570254bf" xlink:to="loc_abvx_SaleOfStockDomain_af5a6cb4-a79d-443d-8a0d-0af5895ce4ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RegisteredDirectOfferingMember_020d0650-0103-47b7-bd8c-f4904537c382" xlink:href="abvx-20251231.xsd#abvx_RegisteredDirectOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_SaleOfStockDomain_af5a6cb4-a79d-443d-8a0d-0af5895ce4ae" xlink:to="loc_abvx_RegisteredDirectOfferingMember_020d0650-0103-47b7-bd8c-f4904537c382" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_d00be8d3-5d44-403c-ae3d-bfd6a731b144" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable_5a04552b-e148-4136-bb64-1022dc6d3aa2" xlink:to="loc_srt_CounterpartyNameAxis_d00be8d3-5d44-403c-ae3d-bfd6a731b144" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_d00be8d3-5d44-403c-ae3d-bfd6a731b144_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_d00be8d3-5d44-403c-ae3d-bfd6a731b144" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_d00be8d3-5d44-403c-ae3d-bfd6a731b144_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_4fc9eb33-2169-4d10-ba48-eca99716d298" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_d00be8d3-5d44-403c-ae3d-bfd6a731b144" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_4fc9eb33-2169-4d10-ba48-eca99716d298" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BanquePubliqueDInvestissementBPIMember_9cd4ef0c-c5fe-4f1b-90c1-21e4b2428b63" xlink:href="abvx-20251231.xsd#abvx_BanquePubliqueDInvestissementBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_4fc9eb33-2169-4d10-ba48-eca99716d298" xlink:to="loc_abvx_BanquePubliqueDInvestissementBPIMember_9cd4ef0c-c5fe-4f1b-90c1-21e4b2428b63" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProfitLoss_aec0127e-6b8d-4fde-b41a-e249987e3005" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_3727c861-3787-40da-8ee4-8557a018979d" xlink:to="loc_ifrs-full_ProfitLoss_aec0127e-6b8d-4fde-b41a-e249987e3005" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProceedsFromIssuingShares_1802063c-a58b-4ef5-b865-7fd025a35499" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProceedsFromIssuingShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_3727c861-3787-40da-8ee4-8557a018979d" xlink:to="loc_ifrs-full_ProceedsFromIssuingShares_1802063c-a58b-4ef5-b865-7fd025a35499" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProceedsFromBorrowingsClassifiedAsFinancingActivities_bf28e84e-a047-46ba-bfb9-2f77bb98f8a2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProceedsFromBorrowingsClassifiedAsFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_3727c861-3787-40da-8ee4-8557a018979d" xlink:to="loc_ifrs-full_ProceedsFromBorrowingsClassifiedAsFinancingActivities_bf28e84e-a047-46ba-bfb9-2f77bb98f8a2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ProceedsFromResearchTaxCredit_024b1391-8e72-4a5f-aa7e-14b2be6b3fcd" xlink:href="abvx-20251231.xsd#abvx_ProceedsFromResearchTaxCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_3727c861-3787-40da-8ee4-8557a018979d" xlink:to="loc_abvx_ProceedsFromResearchTaxCredit_024b1391-8e72-4a5f-aa7e-14b2be6b3fcd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProceedsFromGovernmentGrantsClassifiedAsFinancingActivities_d77a7f93-dee1-4d27-9526-594ddf93ce3c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProceedsFromGovernmentGrantsClassifiedAsFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_3727c861-3787-40da-8ee4-8557a018979d" xlink:to="loc_ifrs-full_ProceedsFromGovernmentGrantsClassifiedAsFinancingActivities_d77a7f93-dee1-4d27-9526-594ddf93ce3c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ProceedsFromConditionalAdvances_b2d623d7-d526-4b71-b1ff-8589a311367e" xlink:href="abvx-20251231.xsd#abvx_ProceedsFromConditionalAdvances"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_3727c861-3787-40da-8ee4-8557a018979d" xlink:to="loc_abvx_ProceedsFromConditionalAdvances_b2d623d7-d526-4b71-b1ff-8589a311367e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NetProceedsFromSaleOfRoyaltyCertificates_963602ec-79bf-45e0-891c-cc9d3049705d" xlink:href="abvx-20251231.xsd#abvx_NetProceedsFromSaleOfRoyaltyCertificates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_3727c861-3787-40da-8ee4-8557a018979d" xlink:to="loc_abvx_NetProceedsFromSaleOfRoyaltyCertificates_963602ec-79bf-45e0-891c-cc9d3049705d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CashAndCashEquivalentsAndOtherShortTermInvestments_019cd7eb-73d9-7d8a-a7c3-7e8550ba39b4" xlink:href="abvx-20251231.xsd#abvx_CashAndCashEquivalentsAndOtherShortTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_3727c861-3787-40da-8ee4-8557a018979d" xlink:to="loc_abvx_CashAndCashEquivalentsAndOtherShortTermInvestments_019cd7eb-73d9-7d8a-a7c3-7e8550ba39b4" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/SignificanteventsfortheyearsendedDecember3120232024and2025andsubsequenteventsFortheyearended2023Details" xlink:type="simple" xlink:href="abvx-20251231.xsd#SignificanteventsfortheyearsendedDecember3120232024and2025andsubsequenteventsFortheyearended2023Details"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/SignificanteventsfortheyearsendedDecember3120232024and2025andsubsequenteventsFortheyearended2023Details" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_4f2160ed-9398-4159-8a3e-9431996a786a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_4f2160ed-9398-4159-8a3e-9431996a786a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialAgreementAxis_f11ee1aa-c644-4aa9-8db1-a9a44aaaa2c5" xlink:href="abvx-20251231.xsd#abvx_FinancialAgreementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_4f2160ed-9398-4159-8a3e-9431996a786a" xlink:to="loc_abvx_FinancialAgreementAxis_f11ee1aa-c644-4aa9-8db1-a9a44aaaa2c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialAgreementDomain_f11ee1aa-c644-4aa9-8db1-a9a44aaaa2c5_default" xlink:href="abvx-20251231.xsd#abvx_FinancialAgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_FinancialAgreementAxis_f11ee1aa-c644-4aa9-8db1-a9a44aaaa2c5" xlink:to="loc_abvx_FinancialAgreementDomain_f11ee1aa-c644-4aa9-8db1-a9a44aaaa2c5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialAgreementDomain_3b33e393-8817-49f5-9e37-1ec0ea3c494b" xlink:href="abvx-20251231.xsd#abvx_FinancialAgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_FinancialAgreementAxis_f11ee1aa-c644-4aa9-8db1-a9a44aaaa2c5" xlink:to="loc_abvx_FinancialAgreementDomain_3b33e393-8817-49f5-9e37-1ec0ea3c494b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_A130.0MillionCrossOverFinancingFebruary2023Member_a14ac1d7-8642-4bae-bc5e-a3894ba31a70" xlink:href="abvx-20251231.xsd#abvx_A130.0MillionCrossOverFinancingFebruary2023Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FinancialAgreementDomain_3b33e393-8817-49f5-9e37-1ec0ea3c494b" xlink:to="loc_abvx_A130.0MillionCrossOverFinancingFebruary2023Member_a14ac1d7-8642-4bae-bc5e-a3894ba31a70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_A49.2MillionCrossOverFinancingSeptember2022Member_41e98ff5-e04f-403a-8337-77b2894369cf" xlink:href="abvx-20251231.xsd#abvx_A49.2MillionCrossOverFinancingSeptember2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FinancialAgreementDomain_3b33e393-8817-49f5-9e37-1ec0ea3c494b" xlink:to="loc_abvx_A49.2MillionCrossOverFinancingSeptember2022Member_41e98ff5-e04f-403a-8337-77b2894369cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_A150.0MillionFinancingAugust2023Member_98153e11-2c37-4328-badf-0aa3439029d7" xlink:href="abvx-20251231.xsd#abvx_A150.0MillionFinancingAugust2023Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FinancialAgreementDomain_3b33e393-8817-49f5-9e37-1ec0ea3c494b" xlink:to="loc_abvx_A150.0MillionFinancingAugust2023Member_98153e11-2c37-4328-badf-0aa3439029d7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ComponentsOfEquityAxis_5f01a384-9b1d-4582-8120-8d317e191fa1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_4f2160ed-9398-4159-8a3e-9431996a786a" xlink:to="loc_ifrs-full_ComponentsOfEquityAxis_5f01a384-9b1d-4582-8120-8d317e191fa1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ComponentsOfEquityDomain_5f01a384-9b1d-4582-8120-8d317e191fa1_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ComponentsOfEquityAxis_5f01a384-9b1d-4582-8120-8d317e191fa1" xlink:to="loc_ifrs-full_ComponentsOfEquityDomain_5f01a384-9b1d-4582-8120-8d317e191fa1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ComponentsOfEquityDomain_8f94ca90-8cc8-4ed0-8ddb-d2ba0dd08270" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ComponentsOfEquityAxis_5f01a384-9b1d-4582-8120-8d317e191fa1" xlink:to="loc_ifrs-full_ComponentsOfEquityDomain_8f94ca90-8cc8-4ed0-8ddb-d2ba0dd08270" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_SharePremiumMember_a69ad1b5-6e98-4a9e-8387-072f37eb9f01" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SharePremiumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ComponentsOfEquityDomain_8f94ca90-8cc8-4ed0-8ddb-d2ba0dd08270" xlink:to="loc_ifrs-full_SharePremiumMember_a69ad1b5-6e98-4a9e-8387-072f37eb9f01" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_5726150b-87b1-4d15-8a09-1533f91009d5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_4f2160ed-9398-4159-8a3e-9431996a786a" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_5726150b-87b1-4d15-8a09-1533f91009d5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_5726150b-87b1-4d15-8a09-1533f91009d5_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_5726150b-87b1-4d15-8a09-1533f91009d5" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_5726150b-87b1-4d15-8a09-1533f91009d5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_c57574e1-a77d-4d91-969f-45c36e6ebac7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_5726150b-87b1-4d15-8a09-1533f91009d5" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_c57574e1-a77d-4d91-969f-45c36e6ebac7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos1ConvertibleBondLoansTrancheAMember_ba072001-3e39-4199-a98c-3cb4698fb05a" xlink:href="abvx-20251231.xsd#abvx_Kreos1ConvertibleBondLoansTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_c57574e1-a77d-4d91-969f-45c36e6ebac7" xlink:to="loc_abvx_Kreos1ConvertibleBondLoansTrancheAMember_ba072001-3e39-4199-a98c-3cb4698fb05a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos1ConvertibleBondLoansTrancheBMember_3934b5a4-7f21-4ad2-a2e1-fd3bcfcd9406" xlink:href="abvx-20251231.xsd#abvx_Kreos1ConvertibleBondLoansTrancheBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_c57574e1-a77d-4d91-969f-45c36e6ebac7" xlink:to="loc_abvx_Kreos1ConvertibleBondLoansTrancheBMember_3934b5a4-7f21-4ad2-a2e1-fd3bcfcd9406" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingMember_a319e854-9496-44b1-9444-288f19675070" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_c57574e1-a77d-4d91-969f-45c36e6ebac7" xlink:to="loc_abvx_KreosClaretFinancingMember_a319e854-9496-44b1-9444-288f19675070" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_HeightsConvertibleNotesMember_dd5efce1-7e89-4334-876d-e9eacb337606" xlink:href="abvx-20251231.xsd#abvx_HeightsConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_c57574e1-a77d-4d91-969f-45c36e6ebac7" xlink:to="loc_abvx_HeightsConvertibleNotesMember_dd5efce1-7e89-4334-876d-e9eacb337606" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheAMember_103ae38f-be96-4337-bda7-0064012edca5" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_c57574e1-a77d-4d91-969f-45c36e6ebac7" xlink:to="loc_abvx_KreosClaretFinancingTrancheAMember_103ae38f-be96-4337-bda7-0064012edca5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OCEANEMember_5e75d5f5-6358-4c46-917c-0b3c73c2054c" xlink:href="abvx-20251231.xsd#abvx_OCEANEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_c57574e1-a77d-4d91-969f-45c36e6ebac7" xlink:to="loc_abvx_OCEANEMember_5e75d5f5-6358-4c46-917c-0b3c73c2054c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingAndHeightsConvertibleNotesMember_f243d714-df1d-428f-89d9-fbc96c1b18bc" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingAndHeightsConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_c57574e1-a77d-4d91-969f-45c36e6ebac7" xlink:to="loc_abvx_KreosClaretFinancingAndHeightsConvertibleNotesMember_f243d714-df1d-428f-89d9-fbc96c1b18bc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalAxis_cd16f4b3-1b22-4b3f-9dfe-e5111ba16182" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_4f2160ed-9398-4159-8a3e-9431996a786a" xlink:to="loc_ifrs-full_ClassesOfShareCapitalAxis_cd16f4b3-1b22-4b3f-9dfe-e5111ba16182" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalDomain_cd16f4b3-1b22-4b3f-9dfe-e5111ba16182_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfShareCapitalAxis_cd16f4b3-1b22-4b3f-9dfe-e5111ba16182" xlink:to="loc_ifrs-full_ClassesOfShareCapitalDomain_cd16f4b3-1b22-4b3f-9dfe-e5111ba16182_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalDomain_81ecfecb-581f-4359-a6d7-61262160381e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfShareCapitalAxis_cd16f4b3-1b22-4b3f-9dfe-e5111ba16182" xlink:to="loc_ifrs-full_ClassesOfShareCapitalDomain_81ecfecb-581f-4359-a6d7-61262160381e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AmericanDepositorySharesMember_2c67ba44-c9bf-4bdf-ae80-7b7db54b6688" xlink:href="abvx-20251231.xsd#abvx_AmericanDepositorySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfShareCapitalDomain_81ecfecb-581f-4359-a6d7-61262160381e" xlink:to="loc_abvx_AmericanDepositorySharesMember_2c67ba44-c9bf-4bdf-ae80-7b7db54b6688" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OrdinarySharesMember_b5e97169-a592-4021-8a0a-c608bcc82a0e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfShareCapitalDomain_81ecfecb-581f-4359-a6d7-61262160381e" xlink:to="loc_ifrs-full_OrdinarySharesMember_b5e97169-a592-4021-8a0a-c608bcc82a0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_c90e2a2b-44f6-4074-9954-7b566f0415fa" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_4f2160ed-9398-4159-8a3e-9431996a786a" xlink:to="loc_srt_RangeAxis_c90e2a2b-44f6-4074-9954-7b566f0415fa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c90e2a2b-44f6-4074-9954-7b566f0415fa_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_c90e2a2b-44f6-4074-9954-7b566f0415fa" xlink:to="loc_srt_RangeMember_c90e2a2b-44f6-4074-9954-7b566f0415fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_684911bb-2078-4c7a-a060-3f6a33f68d0d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_c90e2a2b-44f6-4074-9954-7b566f0415fa" xlink:to="loc_srt_RangeMember_684911bb-2078-4c7a-a060-3f6a33f68d0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_c2d9ed35-330c-44cd-b1da-548f59f3e756" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_684911bb-2078-4c7a-a060-3f6a33f68d0d" xlink:to="loc_srt_MaximumMember_c2d9ed35-330c-44cd-b1da-548f59f3e756" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsAxis_86a16f4d-4222-47d4-9c03-7af3a2907e78" xlink:href="abvx-20251231.xsd#abvx_WarrantsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_4f2160ed-9398-4159-8a3e-9431996a786a" xlink:to="loc_abvx_WarrantsAxis_86a16f4d-4222-47d4-9c03-7af3a2907e78" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsDomain_86a16f4d-4222-47d4-9c03-7af3a2907e78_default" xlink:href="abvx-20251231.xsd#abvx_WarrantsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_WarrantsAxis_86a16f4d-4222-47d4-9c03-7af3a2907e78" xlink:to="loc_abvx_WarrantsDomain_86a16f4d-4222-47d4-9c03-7af3a2907e78_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsDomain_12ca03ff-7503-4b90-b035-ad5c5bd817e8" xlink:href="abvx-20251231.xsd#abvx_WarrantsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_WarrantsAxis_86a16f4d-4222-47d4-9c03-7af3a2907e78" xlink:to="loc_abvx_WarrantsDomain_12ca03ff-7503-4b90-b035-ad5c5bd817e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosCBSAMember_0cdb8b2c-ea25-4a43-9ab7-7a0b8d7dfeb6" xlink:href="abvx-20251231.xsd#abvx_KreosCBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_WarrantsDomain_12ca03ff-7503-4b90-b035-ad5c5bd817e8" xlink:to="loc_abvx_KreosCBSAMember_0cdb8b2c-ea25-4a43-9ab7-7a0b8d7dfeb6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_df586d1b-804e-4766-9c05-0db5c0a86db3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_4f2160ed-9398-4159-8a3e-9431996a786a" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_df586d1b-804e-4766-9c05-0db5c0a86db3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_df586d1b-804e-4766-9c05-0db5c0a86db3_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_df586d1b-804e-4766-9c05-0db5c0a86db3" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_df586d1b-804e-4766-9c05-0db5c0a86db3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_975fb03d-6e10-4856-ae7f-a5497e046654" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_df586d1b-804e-4766-9c05-0db5c0a86db3" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_975fb03d-6e10-4856-ae7f-a5497e046654" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FreeSharesAGAMember_5b7be167-3091-4d36-ad73-eaa0b67eb602" xlink:href="abvx-20251231.xsd#abvx_FreeSharesAGAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_975fb03d-6e10-4856-ae7f-a5497e046654" xlink:to="loc_abvx_FreeSharesAGAMember_5b7be167-3091-4d36-ad73-eaa0b67eb602" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialAgreementAmount_8f1d6b61-436e-41ef-80fb-6163177198be" xlink:href="abvx-20251231.xsd#abvx_FinancialAgreementAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_FinancialAgreementAmount_8f1d6b61-436e-41ef-80fb-6163177198be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IssueOfEquity_2d7f681a-ff9b-42b0-a7fe-a52137b538e5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IssueOfEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_ifrs-full_IssueOfEquity_2d7f681a-ff9b-42b0-a7fe-a52137b538e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease_b5054313-4b5f-4822-8cff-09e6825f611d" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease_b5054313-4b5f-4822-8cff-09e6825f611d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ParValuePerShare_408e3784-b477-4830-be11-49444bc76dd6" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ParValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_ifrs-full_ParValuePerShare_408e3784-b477-4830-be11-49444bc76dd6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EquityIssuancePercentageOfCurrentShareCapital_8be79708-cc76-47ab-ae73-01e0e6f515c2" xlink:href="abvx-20251231.xsd#abvx_EquityIssuancePercentageOfCurrentShareCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_EquityIssuancePercentageOfCurrentShareCapital_8be79708-cc76-47ab-ae73-01e0e6f515c2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EquityIssuanceSubscriptionPricePerShare_0cfede77-0f98-487d-8d3c-7194f452586d" xlink:href="abvx-20251231.xsd#abvx_EquityIssuanceSubscriptionPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_EquityIssuanceSubscriptionPricePerShare_0cfede77-0f98-487d-8d3c-7194f452586d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ShareIssueRelatedCost_0aad9077-dc6e-4ae8-9718-e333ee2b5cbc" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ShareIssueRelatedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_ifrs-full_ShareIssueRelatedCost_0aad9077-dc6e-4ae8-9718-e333ee2b5cbc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfOtherShareWarrantsRepurchased_1931ed97-a3d6-4f31-bb45-7ce49ff73834" xlink:href="abvx-20251231.xsd#abvx_NumberOfOtherShareWarrantsRepurchased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_NumberOfOtherShareWarrantsRepurchased_1931ed97-a3d6-4f31-bb45-7ce49ff73834" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants_1e2cb7bc-f329-454e-a1a5-80d58010348f" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants_1e2cb7bc-f329-454e-a1a5-80d58010348f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfShareBasedCompensationPlansIssued_b3df8840-47a9-4c3b-a74a-d336f0ae0c7d" xlink:href="abvx-20251231.xsd#abvx_NumberOfShareBasedCompensationPlansIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_NumberOfShareBasedCompensationPlansIssued_b3df8840-47a9-4c3b-a74a-d336f0ae0c7d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_b71d0cc6-61b9-4e20-a592-3909efb31778" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_b71d0cc6-61b9-4e20-a592-3909efb31778" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialAgreementNumberOfTransactions_9b2dc97f-ac6f-4133-9bb8-e440853393dd" xlink:href="abvx-20251231.xsd#abvx_FinancialAgreementNumberOfTransactions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_FinancialAgreementNumberOfTransactions_9b2dc97f-ac6f-4133-9bb8-e440853393dd" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsMaximumBorrowingCapacity_9cb21027-4e5a-4508-abe2-e69dd0d00f91" xlink:href="abvx-20251231.xsd#abvx_BorrowingsMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_BorrowingsMaximumBorrowingCapacity_9cb21027-4e5a-4508-abe2-e69dd0d00f91" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AggregateExercisePriceOtherEquityInstrumentsGranted_87fb5006-fc49-4dac-9608-d4fc67a58812" xlink:href="abvx-20251231.xsd#abvx_AggregateExercisePriceOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_AggregateExercisePriceOtherEquityInstrumentsGranted_87fb5006-fc49-4dac-9608-d4fc67a58812" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProceedsFromBorrowingsClassifiedAsFinancingActivities_db06c5d7-9d0d-415d-8e4f-aa7f20b848f7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProceedsFromBorrowingsClassifiedAsFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_ifrs-full_ProceedsFromBorrowingsClassifiedAsFinancingActivities_db06c5d7-9d0d-415d-8e4f-aa7f20b848f7" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RepaymentsOfConvertibleLoansNotes_d49bdc38-9303-47b7-ae8a-94f53cfe5308" xlink:href="abvx-20251231.xsd#abvx_RepaymentsOfConvertibleLoansNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_RepaymentsOfConvertibleLoansNotes_d49bdc38-9303-47b7-ae8a-94f53cfe5308" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ProceedsFromBorrowingsNetOfRefinancingOfExistingIndebteness_62cf4cec-17aa-431a-b8d7-9a4982ad07f6" xlink:href="abvx-20251231.xsd#abvx_ProceedsFromBorrowingsNetOfRefinancingOfExistingIndebteness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_ProceedsFromBorrowingsNetOfRefinancingOfExistingIndebteness_62cf4cec-17aa-431a-b8d7-9a4982ad07f6" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IssuanceOfOtherShareWarrants_ae4e37bb-78f5-4e2b-b08d-fa1f4509bb75" xlink:href="abvx-20251231.xsd#abvx_IssuanceOfOtherShareWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_IssuanceOfOtherShareWarrants_ae4e37bb-78f5-4e2b-b08d-fa1f4509bb75" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfSharesReceivedPerADS_6267e321-f19d-4382-b743-6cc6e7365ff4" xlink:href="abvx-20251231.xsd#abvx_NumberOfSharesReceivedPerADS"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_NumberOfSharesReceivedPerADS_6267e321-f19d-4382-b743-6cc6e7365ff4" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IssueOfEquityOfferingPricePerShare_a351f9af-52e4-441b-97bb-b460e515d994" xlink:href="abvx-20251231.xsd#abvx_IssueOfEquityOfferingPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_IssueOfEquityOfferingPricePerShare_a351f9af-52e4-441b-97bb-b460e515d994" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProceedsFromIssuingShares_caaf49b4-b8ae-4d51-887e-37a6895c2e72" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProceedsFromIssuingShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_ifrs-full_ProceedsFromIssuingShares_caaf49b4-b8ae-4d51-887e-37a6895c2e72" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ProceedsFromIssuingSharesOtherThanThroughExerciseOfWarrants_301d71dd-5f07-4e85-8589-c05a4c915690" xlink:href="abvx-20251231.xsd#abvx_ProceedsFromIssuingSharesOtherThanThroughExerciseOfWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_abvx_ProceedsFromIssuingSharesOtherThanThroughExerciseOfWarrants_301d71dd-5f07-4e85-8589-c05a4c915690" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PaymentsForShareIssueCosts_1ca917fa-0b76-4fd5-b189-7a6f113c6011" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PaymentsForShareIssueCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_cafd87af-5da2-4641-a0b0-39392db3550b" xlink:to="loc_ifrs-full_PaymentsForShareIssueCosts_1ca917fa-0b76-4fd5-b189-7a6f113c6011" xlink:type="arc" order="22"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/SignificanteventsfortheyearsendedDecember3120232024and2025andsubsequenteventsFortheyearended2024Details" xlink:type="simple" xlink:href="abvx-20251231.xsd#SignificanteventsfortheyearsendedDecember3120232024and2025andsubsequenteventsFortheyearended2024Details"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/SignificanteventsfortheyearsendedDecember3120232024and2025andsubsequenteventsFortheyearended2024Details" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable_8ac2c0c6-1416-45a2-8c01-ebe7609ccfec" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable_8ac2c0c6-1416-45a2-8c01-ebe7609ccfec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_51582bdc-32ef-4749-aa04-d5b2cae0beb4" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable_8ac2c0c6-1416-45a2-8c01-ebe7609ccfec" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_51582bdc-32ef-4749-aa04-d5b2cae0beb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_51582bdc-32ef-4749-aa04-d5b2cae0beb4_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_51582bdc-32ef-4749-aa04-d5b2cae0beb4" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_51582bdc-32ef-4749-aa04-d5b2cae0beb4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_01f2dc4b-0792-4a7a-a0be-20232fa9a1b0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_51582bdc-32ef-4749-aa04-d5b2cae0beb4" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_01f2dc4b-0792-4a7a-a0be-20232fa9a1b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA2024Member_7dc4b2d8-d003-4493-a44c-55374801634f" xlink:href="abvx-20251231.xsd#abvx_AGA2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_01f2dc4b-0792-4a7a-a0be-20232fa9a1b0" xlink:to="loc_abvx_AGA2024Member_7dc4b2d8-d003-4493-a44c-55374801634f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20246Member_1a5794d5-2d46-46d3-8156-3735deb4ffa6" xlink:href="abvx-20251231.xsd#abvx_AGA20246Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_01f2dc4b-0792-4a7a-a0be-20232fa9a1b0" xlink:to="loc_abvx_AGA20246Member_1a5794d5-2d46-46d3-8156-3735deb4ffa6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20241Member_f02ff7ef-f028-4f3a-b73d-c2b1783a35b9" xlink:href="abvx-20251231.xsd#abvx_BSA20241Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_01f2dc4b-0792-4a7a-a0be-20232fa9a1b0" xlink:to="loc_abvx_BSA20241Member_f02ff7ef-f028-4f3a-b73d-c2b1783a35b9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesAxis_fb6ef457-c6fd-459a-b68d-205708d2c7cb" xlink:href="abvx-20251231.xsd#abvx_TranchesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable_8ac2c0c6-1416-45a2-8c01-ebe7609ccfec" xlink:to="loc_abvx_TranchesAxis_fb6ef457-c6fd-459a-b68d-205708d2c7cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesDomain_fb6ef457-c6fd-459a-b68d-205708d2c7cb_default" xlink:href="abvx-20251231.xsd#abvx_TranchesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_TranchesAxis_fb6ef457-c6fd-459a-b68d-205708d2c7cb" xlink:to="loc_abvx_TranchesDomain_fb6ef457-c6fd-459a-b68d-205708d2c7cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesDomain_a99b33ce-454e-4d90-9f38-5b9ae17cc668" xlink:href="abvx-20251231.xsd#abvx_TranchesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_TranchesAxis_fb6ef457-c6fd-459a-b68d-205708d2c7cb" xlink:to="loc_abvx_TranchesDomain_a99b33ce-454e-4d90-9f38-5b9ae17cc668" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheOneMember_ca613633-c968-4916-888c-f38a14e7da1e" xlink:href="abvx-20251231.xsd#abvx_TrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_a99b33ce-454e-4d90-9f38-5b9ae17cc668" xlink:to="loc_abvx_TrancheOneMember_ca613633-c968-4916-888c-f38a14e7da1e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheTwoMember_4adaa04d-2473-4958-ba28-d5b6c013f823" xlink:href="abvx-20251231.xsd#abvx_TrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_a99b33ce-454e-4d90-9f38-5b9ae17cc668" xlink:to="loc_abvx_TrancheTwoMember_4adaa04d-2473-4958-ba28-d5b6c013f823" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheThreeMember_5a4f1005-5aef-40a2-91fa-0ee8525dd5ae" xlink:href="abvx-20251231.xsd#abvx_TrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_a99b33ce-454e-4d90-9f38-5b9ae17cc668" xlink:to="loc_abvx_TrancheThreeMember_5a4f1005-5aef-40a2-91fa-0ee8525dd5ae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_f737c7c6-4827-445e-9e72-40045f243f8a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable_8ac2c0c6-1416-45a2-8c01-ebe7609ccfec" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_f737c7c6-4827-445e-9e72-40045f243f8a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_f737c7c6-4827-445e-9e72-40045f243f8a_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_f737c7c6-4827-445e-9e72-40045f243f8a" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_f737c7c6-4827-445e-9e72-40045f243f8a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_891bce34-cc65-40a8-b2f0-15f836783a74" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_f737c7c6-4827-445e-9e72-40045f243f8a" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_891bce34-cc65-40a8-b2f0-15f836783a74" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheBMember_d25eee13-9de1-43ec-9d7a-66db54ae1f58" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_891bce34-cc65-40a8-b2f0-15f836783a74" xlink:to="loc_abvx_KreosClaretFinancingTrancheBMember_d25eee13-9de1-43ec-9d7a-66db54ae1f58" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheCMember_89ef56c2-1aac-4a7c-b49d-bfff813b9cb5" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_891bce34-cc65-40a8-b2f0-15f836783a74" xlink:to="loc_abvx_KreosClaretFinancingTrancheCMember_89ef56c2-1aac-4a7c-b49d-bfff813b9cb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheBAndCMember_64fc0902-24d7-43a8-ad55-e5a8f3a459a1" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheBAndCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_891bce34-cc65-40a8-b2f0-15f836783a74" xlink:to="loc_abvx_KreosClaretFinancingTrancheBAndCMember_64fc0902-24d7-43a8-ad55-e5a8f3a459a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_51c3c5e1-78c2-4fd0-a8e6-d4c176341d36" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable_8ac2c0c6-1416-45a2-8c01-ebe7609ccfec" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_51c3c5e1-78c2-4fd0-a8e6-d4c176341d36" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_51c3c5e1-78c2-4fd0-a8e6-d4c176341d36_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_51c3c5e1-78c2-4fd0-a8e6-d4c176341d36" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_51c3c5e1-78c2-4fd0-a8e6-d4c176341d36_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_159a014c-d774-4d09-bb2c-892fabbfa1a8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_51c3c5e1-78c2-4fd0-a8e6-d4c176341d36" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_159a014c-d774-4d09-bb2c-892fabbfa1a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RNPVIRConditionalAdvanceBPIMember_cd27b71f-f3f2-4aed-9347-6cecaae4fd63" xlink:href="abvx-20251231.xsd#abvx_RNPVIRConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_159a014c-d774-4d09-bb2c-892fabbfa1a8" xlink:to="loc_abvx_RNPVIRConditionalAdvanceBPIMember_cd27b71f-f3f2-4aed-9347-6cecaae4fd63" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CARENAConditionalAdvanceBPIMember_ce919239-7900-4ce4-858e-c39e3257b9cc" xlink:href="abvx-20251231.xsd#abvx_CARENAConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_159a014c-d774-4d09-bb2c-892fabbfa1a8" xlink:to="loc_abvx_CARENAConditionalAdvanceBPIMember_ce919239-7900-4ce4-858e-c39e3257b9cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RNPVIRConditionalAdvanceBPIAndCARENAConditionalAdvanceBPIMember_23e63341-60d4-49ca-ba60-1479122b9848" xlink:href="abvx-20251231.xsd#abvx_RNPVIRConditionalAdvanceBPIAndCARENAConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_159a014c-d774-4d09-bb2c-892fabbfa1a8" xlink:to="loc_abvx_RNPVIRConditionalAdvanceBPIAndCARENAConditionalAdvanceBPIMember_23e63341-60d4-49ca-ba60-1479122b9848" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SaleOfStockAxis_5bf3019f-0075-482b-b9fd-2e655f146f40" xlink:href="abvx-20251231.xsd#abvx_SaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable_8ac2c0c6-1416-45a2-8c01-ebe7609ccfec" xlink:to="loc_abvx_SaleOfStockAxis_5bf3019f-0075-482b-b9fd-2e655f146f40" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SaleOfStockDomain_5bf3019f-0075-482b-b9fd-2e655f146f40_default" xlink:href="abvx-20251231.xsd#abvx_SaleOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_SaleOfStockAxis_5bf3019f-0075-482b-b9fd-2e655f146f40" xlink:to="loc_abvx_SaleOfStockDomain_5bf3019f-0075-482b-b9fd-2e655f146f40_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SaleOfStockDomain_857307c1-09d7-4d8c-9027-1103349efa34" xlink:href="abvx-20251231.xsd#abvx_SaleOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_SaleOfStockAxis_5bf3019f-0075-482b-b9fd-2e655f146f40" xlink:to="loc_abvx_SaleOfStockDomain_857307c1-09d7-4d8c-9027-1103349efa34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AtTheMarketATMProgramMember_38e54fc7-4a55-4735-a288-e520dc42b723" xlink:href="abvx-20251231.xsd#abvx_AtTheMarketATMProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_SaleOfStockDomain_857307c1-09d7-4d8c-9027-1103349efa34" xlink:to="loc_abvx_AtTheMarketATMProgramMember_38e54fc7-4a55-4735-a288-e520dc42b723" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfFreeSharesPlansIssued_f0704c72-c7d7-4ddc-8bfd-f0bc87a8fb9a" xlink:href="abvx-20251231.xsd#abvx_NumberOfFreeSharesPlansIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_abvx_NumberOfFreeSharesPlansIssued_f0704c72-c7d7-4ddc-8bfd-f0bc87a8fb9a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_9a6d37bd-d97b-462b-943c-ee08bff4e0c8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_9a6d37bd-d97b-462b-943c-ee08bff4e0c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentage_a01f4d89-4f36-4c4d-a4fb-42063d7b9931" xlink:href="abvx-20251231.xsd#abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentage_a01f4d89-4f36-4c4d-a4fb-42063d7b9931" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPeriod_5946f9e7-6930-4e9a-9a75-7f27d12c884e" xlink:href="abvx-20251231.xsd#abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPeriod_5946f9e7-6930-4e9a-9a75-7f27d12c884e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProceedsFromBorrowingsClassifiedAsFinancingActivities_9a251a40-7208-4585-b741-f55f4ee80e90" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProceedsFromBorrowingsClassifiedAsFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_ifrs-full_ProceedsFromBorrowingsClassifiedAsFinancingActivities_9a251a40-7208-4585-b741-f55f4ee80e90" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsMaximumBorrowingCapacity_42a531ce-1383-4cb5-ba7a-48aaaf026381" xlink:href="abvx-20251231.xsd#abvx_BorrowingsMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_abvx_BorrowingsMaximumBorrowingCapacity_42a531ce-1383-4cb5-ba7a-48aaaf026381" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ParValuePerShare_c3abb54a-46a6-4913-90a1-e3d54d62c619" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ParValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_ifrs-full_ParValuePerShare_c3abb54a-46a6-4913-90a1-e3d54d62c619" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ProceedsFromConditionalAdvances_120e7152-b9fb-4807-88ad-12d2d6025d7e" xlink:href="abvx-20251231.xsd#abvx_ProceedsFromConditionalAdvances"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_abvx_ProceedsFromConditionalAdvances_120e7152-b9fb-4807-88ad-12d2d6025d7e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProceedsFromGovernmentGrantsClassifiedAsFinancingActivities_ba95cc77-a0e5-45a5-bf9d-cf6e3baacc8a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProceedsFromGovernmentGrantsClassifiedAsFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_ifrs-full_ProceedsFromGovernmentGrantsClassifiedAsFinancingActivities_ba95cc77-a0e5-45a5-bf9d-cf6e3baacc8a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PercentageOfConditionalAdvancesWaived_9981f06a-0dba-495c-93a8-288699cfe73d" xlink:href="abvx-20251231.xsd#abvx_PercentageOfConditionalAdvancesWaived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_abvx_PercentageOfConditionalAdvancesWaived_9981f06a-0dba-495c-93a8-288699cfe73d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RevenueFromGovernmentGrants_4edcf9cf-48fd-44da-b7b6-a577eb90f592" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RevenueFromGovernmentGrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_ifrs-full_RevenueFromGovernmentGrants_4edcf9cf-48fd-44da-b7b6-a577eb90f592" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfADSPerOrdinaryShares_4ec551c6-67d8-4e64-93a6-e1cb190b2c6b" xlink:href="abvx-20251231.xsd#abvx_NumberOfADSPerOrdinaryShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_abvx_NumberOfADSPerOrdinaryShares_4ec551c6-67d8-4e64-93a6-e1cb190b2c6b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExpectedProceedsFromShareIssuance_e3438e42-66e8-4fed-a5b7-a25049a33b13" xlink:href="abvx-20251231.xsd#abvx_ExpectedProceedsFromShareIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_abvx_ExpectedProceedsFromShareIssuance_e3438e42-66e8-4fed-a5b7-a25049a33b13" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExpectedProceedsFromShareIssuanceShelfRegistration_e2757e53-8000-4aa9-aa8b-3f73f6c176b6" xlink:href="abvx-20251231.xsd#abvx_ExpectedProceedsFromShareIssuanceShelfRegistration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_5fc8bf59-7fd4-47e0-b270-ecd573debcdf" xlink:to="loc_abvx_ExpectedProceedsFromShareIssuanceShelfRegistration_e2757e53-8000-4aa9-aa8b-3f73f6c176b6" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/SignificanteventsfortheyearsendedDecember3120232024and2025andsubsequenteventsFortheyearended2025Details" xlink:type="simple" xlink:href="abvx-20251231.xsd#SignificanteventsfortheyearsendedDecember3120232024and2025andsubsequenteventsFortheyearended2025Details"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/SignificanteventsfortheyearsendedDecember3120232024and2025andsubsequenteventsFortheyearended2025Details" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_019beae7-6ccc-7a24-8454-790efec75929" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_019beae7-6ccc-7a24-8454-790efec75929" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019beae7-6ccc-72c2-bc77-4407f8420694" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_019beae7-6ccc-7a24-8454-790efec75929" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019beae7-6ccc-72c2-bc77-4407f8420694" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019beae7-6ccc-72c2-bc77-4407f8420694_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019beae7-6ccc-72c2-bc77-4407f8420694" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019beae7-6ccc-72c2-bc77-4407f8420694_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019beae7-6ccc-78b8-962b-256576f0b913" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019beae7-6ccc-72c2-bc77-4407f8420694" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019beae7-6ccc-78b8-962b-256576f0b913" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ShareSubscriptionWarrantsBSAMember_019beae7-6ccc-783a-977a-6180c16723b3" xlink:href="abvx-20251231.xsd#abvx_ShareSubscriptionWarrantsBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019beae7-6ccc-78b8-962b-256576f0b913" xlink:to="loc_abvx_ShareSubscriptionWarrantsBSAMember_019beae7-6ccc-783a-977a-6180c16723b3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA2025Member_019beae7-6ccc-78a9-a5bf-e0d9be16f179" xlink:href="abvx-20251231.xsd#abvx_AGA2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019beae7-6ccc-78b8-962b-256576f0b913" xlink:to="loc_abvx_AGA2025Member_019beae7-6ccc-78a9-a5bf-e0d9be16f179" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20252Member_019beae7-6ccc-7672-be26-7289d0b37b10" xlink:href="abvx-20251231.xsd#abvx_AGA20252Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019beae7-6ccc-78b8-962b-256576f0b913" xlink:to="loc_abvx_AGA20252Member_019beae7-6ccc-7672-be26-7289d0b37b10" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20255Member_019beae7-6ccc-777d-8748-a2c3221cba69" xlink:href="abvx-20251231.xsd#abvx_AGA20255Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019beae7-6ccc-78b8-962b-256576f0b913" xlink:to="loc_abvx_AGA20255Member_019beae7-6ccc-777d-8748-a2c3221cba69" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20251Member_019beae7-6ccc-7dd0-b7e7-8f8cd4aea026" xlink:href="abvx-20251231.xsd#abvx_AGA20251Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019beae7-6ccc-78b8-962b-256576f0b913" xlink:to="loc_abvx_AGA20251Member_019beae7-6ccc-7dd0-b7e7-8f8cd4aea026" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_019beae7-6ccc-737f-9858-58742dc2ad97" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_019beae7-6ccc-7a24-8454-790efec75929" xlink:to="loc_srt_TitleOfIndividualAxis_019beae7-6ccc-737f-9858-58742dc2ad97" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019beae7-6ccc-737f-9858-58742dc2ad97_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_019beae7-6ccc-737f-9858-58742dc2ad97" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019beae7-6ccc-737f-9858-58742dc2ad97_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019beae7-6ccc-7454-9dd1-9b51a83a2bb7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_019beae7-6ccc-737f-9858-58742dc2ad97" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019beae7-6ccc-7454-9dd1-9b51a83a2bb7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BoardMemberMember_019beae7-6ccc-78b3-aaf5-037e9eb4142e" xlink:href="abvx-20251231.xsd#abvx_BoardMemberMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019beae7-6ccc-7454-9dd1-9b51a83a2bb7" xlink:to="loc_abvx_BoardMemberMember_019beae7-6ccc-78b3-aaf5-037e9eb4142e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesAxis_019beae7-6ccc-779f-a3da-d8d1e3ccb0e5" xlink:href="abvx-20251231.xsd#abvx_TranchesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_019beae7-6ccc-7a24-8454-790efec75929" xlink:to="loc_abvx_TranchesAxis_019beae7-6ccc-779f-a3da-d8d1e3ccb0e5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesDomain_019beae7-6ccc-779f-a3da-d8d1e3ccb0e5_default" xlink:href="abvx-20251231.xsd#abvx_TranchesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_TranchesAxis_019beae7-6ccc-779f-a3da-d8d1e3ccb0e5" xlink:to="loc_abvx_TranchesDomain_019beae7-6ccc-779f-a3da-d8d1e3ccb0e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesDomain_019beae7-6ccc-7910-aced-3fef8e457739" xlink:href="abvx-20251231.xsd#abvx_TranchesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_TranchesAxis_019beae7-6ccc-779f-a3da-d8d1e3ccb0e5" xlink:to="loc_abvx_TranchesDomain_019beae7-6ccc-7910-aced-3fef8e457739" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheOneMember_019beae7-6ccc-792b-8deb-6a3ec85d5b1b" xlink:href="abvx-20251231.xsd#abvx_TrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_019beae7-6ccc-7910-aced-3fef8e457739" xlink:to="loc_abvx_TrancheOneMember_019beae7-6ccc-792b-8deb-6a3ec85d5b1b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheTwoMember_019beae7-6ccc-7e88-988d-657b9a66a580" xlink:href="abvx-20251231.xsd#abvx_TrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_019beae7-6ccc-7910-aced-3fef8e457739" xlink:to="loc_abvx_TrancheTwoMember_019beae7-6ccc-7e88-988d-657b9a66a580" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheThreeMember_019beae7-6ccc-77e9-928c-153784076a25" xlink:href="abvx-20251231.xsd#abvx_TrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_019beae7-6ccc-7910-aced-3fef8e457739" xlink:to="loc_abvx_TrancheThreeMember_019beae7-6ccc-77e9-928c-153784076a25" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_019beae9-d416-74d2-bbf7-dec2ee122c9d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_019beae7-6ccc-7a24-8454-790efec75929" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_019beae9-d416-74d2-bbf7-dec2ee122c9d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019beae9-d416-74d2-bbf7-dec2ee122c9d_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019beae9-d416-74d2-bbf7-dec2ee122c9d" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019beae9-d416-74d2-bbf7-dec2ee122c9d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019beae9-d416-70a6-b96e-afe18a5d5960" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019beae9-d416-74d2-bbf7-dec2ee122c9d" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019beae9-d416-70a6-b96e-afe18a5d5960" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_HeightsConvertibleNotesMember_019beae9-d416-7e5b-8ef9-6455466c0467" xlink:href="abvx-20251231.xsd#abvx_HeightsConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019beae9-d416-70a6-b96e-afe18a5d5960" xlink:to="loc_abvx_HeightsConvertibleNotesMember_019beae9-d416-7e5b-8ef9-6455466c0467" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheAMember_019beae9-d416-740a-b00a-8208ac4028bc" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019beae9-d416-70a6-b96e-afe18a5d5960" xlink:to="loc_abvx_KreosClaretFinancingTrancheAMember_019beae9-d416-740a-b00a-8208ac4028bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosABCBSAMember_019beae9-d416-7d0c-949a-b843769e76d0" xlink:href="abvx-20251231.xsd#abvx_KreosABCBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019beae9-d416-70a6-b96e-afe18a5d5960" xlink:to="loc_abvx_KreosABCBSAMember_019beae9-d416-7d0c-949a-b843769e76d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingBAndCMember_019c4350-fd31-774c-9664-d81f4883a6c6" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingBAndCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019beae9-d416-70a6-b96e-afe18a5d5960" xlink:to="loc_abvx_KreosClaretFinancingBAndCMember_019c4350-fd31-774c-9664-d81f4883a6c6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalAxis_019beae9-d416-7faf-9ada-fd3445ec4c3f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_019beae7-6ccc-7a24-8454-790efec75929" xlink:to="loc_ifrs-full_ClassesOfShareCapitalAxis_019beae9-d416-7faf-9ada-fd3445ec4c3f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalDomain_019beae9-d416-7faf-9ada-fd3445ec4c3f_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfShareCapitalAxis_019beae9-d416-7faf-9ada-fd3445ec4c3f" xlink:to="loc_ifrs-full_ClassesOfShareCapitalDomain_019beae9-d416-7faf-9ada-fd3445ec4c3f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalDomain_019beae9-d416-79d4-8672-2b4c73b1be67" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfShareCapitalAxis_019beae9-d416-7faf-9ada-fd3445ec4c3f" xlink:to="loc_ifrs-full_ClassesOfShareCapitalDomain_019beae9-d416-79d4-8672-2b4c73b1be67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AmericanDepositorySharesMember_019beae9-f264-7bb7-ad1e-0bf70a0ac702" xlink:href="abvx-20251231.xsd#abvx_AmericanDepositorySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfShareCapitalDomain_019beae9-d416-79d4-8672-2b4c73b1be67" xlink:to="loc_abvx_AmericanDepositorySharesMember_019beae9-f264-7bb7-ad1e-0bf70a0ac702" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OrdinarySharesMember_019beae9-d416-77e2-b903-c9f9d88e741b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfShareCapitalDomain_019beae9-d416-79d4-8672-2b4c73b1be67" xlink:to="loc_ifrs-full_OrdinarySharesMember_019beae9-d416-77e2-b903-c9f9d88e741b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_019beae7-6ccc-75a5-bbca-241480c59f9c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_019beae7-6ccc-75a5-bbca-241480c59f9c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPeriod_019beae7-6ccc-70db-8b79-1ae3c2fe19c8" xlink:href="abvx-20251231.xsd#abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPeriod_019beae7-6ccc-70db-8b79-1ae3c2fe19c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentage_019beae7-6ccc-731a-bbf7-999e4ec5b59b" xlink:href="abvx-20251231.xsd#abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentage_019beae7-6ccc-731a-bbf7-999e4ec5b59b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfFreeSharesPlansIssued_019beae7-6ccc-726f-93b1-2c039ca9687c" xlink:href="abvx-20251231.xsd#abvx_NumberOfFreeSharesPlansIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_abvx_NumberOfFreeSharesPlansIssued_019beae7-6ccc-726f-93b1-2c039ca9687c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SharePrice1_019beae9-0f2a-7f6d-ba93-f956cc92553b" xlink:href="abvx-20251231.xsd#abvx_SharePrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_abvx_SharePrice1_019beae9-0f2a-7f6d-ba93-f956cc92553b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseInNumberOfOrdinarySharesIssued_019beae9-d416-7e0c-9018-d43e5dd65a71" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseInNumberOfOrdinarySharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_ifrs-full_IncreaseDecreaseInNumberOfOrdinarySharesIssued_019beae9-d416-7e0c-9018-d43e5dd65a71" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IssueOfEquityOfferingPricePerShare_019beae9-f264-77df-ba76-a04a73f703b1" xlink:href="abvx-20251231.xsd#abvx_IssueOfEquityOfferingPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_abvx_IssueOfEquityOfferingPricePerShare_019beae9-f264-77df-ba76-a04a73f703b1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClosingForeignExchangeRate_019beae9-f264-7b75-a9f6-cc32ec1cf61d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClosingForeignExchangeRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_ifrs-full_ClosingForeignExchangeRate_019beae9-f264-7b75-a9f6-cc32ec1cf61d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProceedsFromIssueOfOrdinaryShares_019beae9-f264-7e53-8306-72dda9862dee" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProceedsFromIssueOfOrdinaryShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_ifrs-full_ProceedsFromIssueOfOrdinaryShares_019beae9-f264-7e53-8306-72dda9862dee" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NetProceedsFromIssueOfOrdinaryShares_019beae9-f264-78f3-b9cd-b6618fd09ce2" xlink:href="abvx-20251231.xsd#abvx_NetProceedsFromIssueOfOrdinaryShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_abvx_NetProceedsFromIssueOfOrdinaryShares_019beae9-f264-78f3-b9cd-b6618fd09ce2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProceedsFromIssuingOtherEquityInstruments_019beae9-f264-7c52-ac40-d6241b5e91e8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProceedsFromIssuingOtherEquityInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_ifrs-full_ProceedsFromIssuingOtherEquityInstruments_019beae9-f264-7c52-ac40-d6241b5e91e8" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfConvertibleNotesConverted_019beae9-d416-7ba4-97d7-6cc889342499" xlink:href="abvx-20251231.xsd#abvx_NumberOfConvertibleNotesConverted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_abvx_NumberOfConvertibleNotesConverted_019beae9-d416-7ba4-97d7-6cc889342499" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NotionalAmount_019beae9-d416-7008-a8e9-02a31311f8d0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_ifrs-full_NotionalAmount_019beae9-d416-7008-a8e9-02a31311f8d0" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsFixedConversionPrice_019beae9-d416-7539-a8fd-7b723075c344" xlink:href="abvx-20251231.xsd#abvx_BorrowingsFixedConversionPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_abvx_BorrowingsFixedConversionPrice_019beae9-d416-7539-a8fd-7b723075c344" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RepaymentsOfBorrowingsClassifiedAsFinancingActivities_019c434f-4789-7cd8-8089-4fd76d189379" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RepaymentsOfBorrowingsClassifiedAsFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019beae7-6ccc-709e-afbd-8db8e488e804" xlink:to="loc_ifrs-full_RepaymentsOfBorrowingsClassifiedAsFinancingActivities_019c434f-4789-7cd8-8089-4fd76d189379" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/SignificanteventsfortheyearsendedDecember3120232024and2025andsubsequenteventsSubsequenteventsDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#SignificanteventsfortheyearsendedDecember3120232024and2025andsubsequenteventsSubsequenteventsDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/SignificanteventsfortheyearsendedDecember3120232024and2025andsubsequenteventsSubsequenteventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019cc310-7e3e-732d-9556-fdae2a74f98b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_019cc310-7e3e-7fa3-99c2-f893b022fa45" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019cc310-7e3e-732d-9556-fdae2a74f98b" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_019cc310-7e3e-7fa3-99c2-f893b022fa45" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NonadjustingEventsAfterReportingPeriodAxis_019cc310-7e3e-75be-a2fd-6c43d009b905" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NonadjustingEventsAfterReportingPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_019cc310-7e3e-7fa3-99c2-f893b022fa45" xlink:to="loc_ifrs-full_NonadjustingEventsAfterReportingPeriodAxis_019cc310-7e3e-75be-a2fd-6c43d009b905" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_019cc310-7e3e-75be-a2fd-6c43d009b905_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NonadjustingEventsAfterReportingPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_NonadjustingEventsAfterReportingPeriodAxis_019cc310-7e3e-75be-a2fd-6c43d009b905" xlink:to="loc_ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_019cc310-7e3e-75be-a2fd-6c43d009b905_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_019cc310-7e3e-7831-9c77-e4dc45955268" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NonadjustingEventsAfterReportingPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_NonadjustingEventsAfterReportingPeriodAxis_019cc310-7e3e-75be-a2fd-6c43d009b905" xlink:to="loc_ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_019cc310-7e3e-7831-9c77-e4dc45955268" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_MajorShareBasedTransactionsMember_019cc310-7e3e-7fcc-a08c-9776db2751e1" xlink:href="abvx-20251231.xsd#abvx_MajorShareBasedTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_019cc310-7e3e-7831-9c77-e4dc45955268" xlink:to="loc_abvx_MajorShareBasedTransactionsMember_019cc310-7e3e-7fcc-a08c-9776db2751e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CSOSettlementAgreementMember_019cf67d-61f0-7afa-aa51-54e74e204290" xlink:href="abvx-20251231.xsd#abvx_CSOSettlementAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_019cc310-7e3e-7831-9c77-e4dc45955268" xlink:to="loc_abvx_CSOSettlementAgreementMember_019cf67d-61f0-7afa-aa51-54e74e204290" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019cc310-7e3e-7e57-822a-268a31b83ac6" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_019cc310-7e3e-7fa3-99c2-f893b022fa45" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019cc310-7e3e-7e57-822a-268a31b83ac6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019cc310-7e3e-7e57-822a-268a31b83ac6_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019cc310-7e3e-7e57-822a-268a31b83ac6" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019cc310-7e3e-7e57-822a-268a31b83ac6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019cc310-7e3e-7a7f-a7df-4a3a7e02ace7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019cc310-7e3e-7e57-822a-268a31b83ac6" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019cc310-7e3e-7a7f-a7df-4a3a7e02ace7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FreeSharesAGAMember_019cc311-13dd-7262-a8bd-33d9223aa097" xlink:href="abvx-20251231.xsd#abvx_FreeSharesAGAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019cc310-7e3e-7a7f-a7df-4a3a7e02ace7" xlink:to="loc_abvx_FreeSharesAGAMember_019cc311-13dd-7262-a8bd-33d9223aa097" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ShareSubscriptionWarrantsBSAMember_019cfbac-e289-7246-a765-ceab850e49c7" xlink:href="abvx-20251231.xsd#abvx_ShareSubscriptionWarrantsBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019cc310-7e3e-7a7f-a7df-4a3a7e02ace7" xlink:to="loc_abvx_ShareSubscriptionWarrantsBSAMember_019cfbac-e289-7246-a765-ceab850e49c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesAxis_019cc310-7e3e-79c4-970b-b8c4fab8a7e2" xlink:href="abvx-20251231.xsd#abvx_TranchesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_019cc310-7e3e-7fa3-99c2-f893b022fa45" xlink:to="loc_abvx_TranchesAxis_019cc310-7e3e-79c4-970b-b8c4fab8a7e2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesDomain_019cc310-7e3e-79c4-970b-b8c4fab8a7e2_default" xlink:href="abvx-20251231.xsd#abvx_TranchesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_TranchesAxis_019cc310-7e3e-79c4-970b-b8c4fab8a7e2" xlink:to="loc_abvx_TranchesDomain_019cc310-7e3e-79c4-970b-b8c4fab8a7e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesDomain_019cc310-7e3e-7ba1-9bdd-7fe3cf8977d7" xlink:href="abvx-20251231.xsd#abvx_TranchesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_TranchesAxis_019cc310-7e3e-79c4-970b-b8c4fab8a7e2" xlink:to="loc_abvx_TranchesDomain_019cc310-7e3e-7ba1-9bdd-7fe3cf8977d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheOneMember_019cc310-7e3e-7c17-ae22-024a7b8a6722" xlink:href="abvx-20251231.xsd#abvx_TrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_019cc310-7e3e-7ba1-9bdd-7fe3cf8977d7" xlink:to="loc_abvx_TrancheOneMember_019cc310-7e3e-7c17-ae22-024a7b8a6722" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheTwoMember_019cc310-7e3e-71db-966a-1b4eed96bdf8" xlink:href="abvx-20251231.xsd#abvx_TrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_019cc310-7e3e-7ba1-9bdd-7fe3cf8977d7" xlink:to="loc_abvx_TrancheTwoMember_019cc310-7e3e-71db-966a-1b4eed96bdf8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheThreeMember_019cc310-7e3e-7e20-8304-6ec61f0a64c7" xlink:href="abvx-20251231.xsd#abvx_TrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_019cc310-7e3e-7ba1-9bdd-7fe3cf8977d7" xlink:to="loc_abvx_TrancheThreeMember_019cc310-7e3e-7e20-8304-6ec61f0a64c7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_019cfbad-625a-742f-9a0b-aace8ce1ae5d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_019cc310-7e3e-7fa3-99c2-f893b022fa45" xlink:to="loc_srt_TitleOfIndividualAxis_019cfbad-625a-742f-9a0b-aace8ce1ae5d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cfbad-625a-742f-9a0b-aace8ce1ae5d_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_019cfbad-625a-742f-9a0b-aace8ce1ae5d" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cfbad-625a-742f-9a0b-aace8ce1ae5d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cfbad-625a-7c94-b2de-94355fb80ccb" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_019cfbad-625a-742f-9a0b-aace8ce1ae5d" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cfbad-625a-7c94-b2de-94355fb80ccb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BoardMemberMember_019cfbad-625a-7984-ba13-57d9adde4a01" xlink:href="abvx-20251231.xsd#abvx_BoardMemberMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019cfbad-625a-7c94-b2de-94355fb80ccb" xlink:to="loc_abvx_BoardMemberMember_019cfbad-625a-7984-ba13-57d9adde4a01" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_019cc310-7e3e-719d-a9c7-6a8d629f6630" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019cc310-7e3e-732d-9556-fdae2a74f98b" xlink:to="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_019cc310-7e3e-719d-a9c7-6a8d629f6630" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentage_019cc310-7e3e-7140-a5c2-96c572e08186" xlink:href="abvx-20251231.xsd#abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019cc310-7e3e-732d-9556-fdae2a74f98b" xlink:to="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentage_019cc310-7e3e-7140-a5c2-96c572e08186" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPeriod_019cc310-7e3e-7f77-83f3-b8ce3e0220cd" xlink:href="abvx-20251231.xsd#abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019cc310-7e3e-732d-9556-fdae2a74f98b" xlink:to="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPeriod_019cc310-7e3e-7f77-83f3-b8ce3e0220cd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_KeyManagementPersonnelCompensationTerminationBenefits_019cf692-b2c9-788f-9afd-70706d534515" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_KeyManagementPersonnelCompensationTerminationBenefits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019cc310-7e3e-732d-9556-fdae2a74f98b" xlink:to="loc_ifrs-full_KeyManagementPersonnelCompensationTerminationBenefits_019cf692-b2c9-788f-9afd-70706d534515" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KeyManagementPersonnelCompensationContractualSeveranceIndemnity_019cf693-fc6e-7752-a36b-9462fa231094" xlink:href="abvx-20251231.xsd#abvx_KeyManagementPersonnelCompensationContractualSeveranceIndemnity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019cc310-7e3e-732d-9556-fdae2a74f98b" xlink:to="loc_abvx_KeyManagementPersonnelCompensationContractualSeveranceIndemnity_019cf693-fc6e-7752-a36b-9462fa231094" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfSharesWaived_019cf6b6-35b3-77f4-88cd-83527ac778c4" xlink:href="abvx-20251231.xsd#abvx_NumberOfSharesWaived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019cc310-7e3e-732d-9556-fdae2a74f98b" xlink:to="loc_abvx_NumberOfSharesWaived_019cf6b6-35b3-77f4-88cd-83527ac778c4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfSharesWithPerformanceConditionsWaived_019cf6b7-2230-7d0c-9761-7eb5fb6494bd" xlink:href="abvx-20251231.xsd#abvx_NumberOfSharesWithPerformanceConditionsWaived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019cc310-7e3e-732d-9556-fdae2a74f98b" xlink:to="loc_abvx_NumberOfSharesWithPerformanceConditionsWaived_019cf6b7-2230-7d0c-9761-7eb5fb6494bd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfSharesLapsed_019cf6b9-29dd-7f86-baef-2520c7ddc7c0" xlink:href="abvx-20251231.xsd#abvx_NumberOfSharesLapsed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019cc310-7e3e-732d-9556-fdae2a74f98b" xlink:to="loc_abvx_NumberOfSharesLapsed_019cf6b9-29dd-7f86-baef-2520c7ddc7c0" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/AccountingprinciplesIntangibleassetsDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#AccountingprinciplesIntangibleassetsDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/AccountingprinciplesIntangibleassetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfIntangibleAssetsLineItems_e064fabd-e523-4374-848b-4f9a0a9a7e73" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfIntangibleAssetsTable_6c5d5940-be46-40bd-b86d-70d08e719a8b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsLineItems_e064fabd-e523-4374-848b-4f9a0a9a7e73" xlink:to="loc_ifrs-full_DisclosureOfIntangibleAssetsTable_6c5d5940-be46-40bd-b86d-70d08e719a8b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillAxis_9b41661c-896a-4fbf-99f0-faa541b6185f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsTable_6c5d5940-be46-40bd-b86d-70d08e719a8b" xlink:to="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillAxis_9b41661c-896a-4fbf-99f0-faa541b6185f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain_9b41661c-896a-4fbf-99f0-faa541b6185f_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillAxis_9b41661c-896a-4fbf-99f0-faa541b6185f" xlink:to="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain_9b41661c-896a-4fbf-99f0-faa541b6185f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain_2defbb06-2e9a-4199-b517-7a5cb73b2f3d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillAxis_9b41661c-896a-4fbf-99f0-faa541b6185f" xlink:to="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain_2defbb06-2e9a-4199-b517-7a5cb73b2f3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OtherIntangibleAssetsMember_77d96577-9a77-441b-bef6-a41c9cc50170" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain_2defbb06-2e9a-4199-b517-7a5cb73b2f3d" xlink:to="loc_ifrs-full_OtherIntangibleAssetsMember_77d96577-9a77-441b-bef6-a41c9cc50170" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ResearchAndDevelopmentCostsRecognitionInitialMeasurementNumberOfCriterias_3b9228f6-ab28-441d-b3d2-1232041967d4" xlink:href="abvx-20251231.xsd#abvx_ResearchAndDevelopmentCostsRecognitionInitialMeasurementNumberOfCriterias"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsLineItems_e064fabd-e523-4374-848b-4f9a0a9a7e73" xlink:to="loc_abvx_ResearchAndDevelopmentCostsRecognitionInitialMeasurementNumberOfCriterias_3b9228f6-ab28-441d-b3d2-1232041967d4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UsefulLifeMeasuredAsPeriodOfTimeIntangibleAssetsOtherThanGoodwill_23283892-3cc7-4657-8468-5ebc839797ab" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UsefulLifeMeasuredAsPeriodOfTimeIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsLineItems_e064fabd-e523-4374-848b-4f9a0a9a7e73" xlink:to="loc_ifrs-full_UsefulLifeMeasuredAsPeriodOfTimeIntangibleAssetsOtherThanGoodwill_23283892-3cc7-4657-8468-5ebc839797ab" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/AccountingprinciplesDisclosureofdepreciationperiodofpropertyplantandequipmentDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#AccountingprinciplesDisclosureofdepreciationperiodofpropertyplantandequipmentDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/AccountingprinciplesDisclosureofdepreciationperiodofpropertyplantandequipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentLineItems_9a14ee8e-0c9b-4c76-9b2e-9ec7e7f2e32c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfPropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentTable_a9711434-40d6-4c3f-b0d1-1bd63fae70a5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentLineItems_9a14ee8e-0c9b-4c76-9b2e-9ec7e7f2e32c" xlink:to="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentTable_a9711434-40d6-4c3f-b0d1-1bd63fae70a5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis_99e7c1c8-10db-4252-9a21-6fba0d752284" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentTable_a9711434-40d6-4c3f-b0d1-1bd63fae70a5" xlink:to="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis_99e7c1c8-10db-4252-9a21-6fba0d752284" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_99e7c1c8-10db-4252-9a21-6fba0d752284_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis_99e7c1c8-10db-4252-9a21-6fba0d752284" xlink:to="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_99e7c1c8-10db-4252-9a21-6fba0d752284_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_8ec3e1c6-7dc2-4567-848b-e61f35835d4d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis_99e7c1c8-10db-4252-9a21-6fba0d752284" xlink:to="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_8ec3e1c6-7dc2-4567-848b-e61f35835d4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_FixturesAndFittingsMember_db567e9a-93d9-4447-980c-9f6845cd9196" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FixturesAndFittingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_8ec3e1c6-7dc2-4567-848b-e61f35835d4d" xlink:to="loc_ifrs-full_FixturesAndFittingsMember_db567e9a-93d9-4447-980c-9f6845cd9196" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IndustrialMaterialsAndEquipmentMember_720e5de2-db2d-4f63-9d17-c51cbe140000" xlink:href="abvx-20251231.xsd#abvx_IndustrialMaterialsAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_8ec3e1c6-7dc2-4567-848b-e61f35835d4d" xlink:to="loc_abvx_IndustrialMaterialsAndEquipmentMember_720e5de2-db2d-4f63-9d17-c51cbe140000" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TechnicalFacilitiesMember_b60907f4-b276-4ca7-afaf-1394bebe1dca" xlink:href="abvx-20251231.xsd#abvx_TechnicalFacilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_8ec3e1c6-7dc2-4567-848b-e61f35835d4d" xlink:to="loc_abvx_TechnicalFacilitiesMember_b60907f4-b276-4ca7-afaf-1394bebe1dca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OfficeEquipmentMember_3624c457-131e-45fe-9e69-94b0c29f3ab4" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OfficeEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_8ec3e1c6-7dc2-4567-848b-e61f35835d4d" xlink:to="loc_ifrs-full_OfficeEquipmentMember_3624c457-131e-45fe-9e69-94b0c29f3ab4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ComputerEquipmentMember_2a80fcbd-f2e3-4302-9645-eb4862cc780d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_8ec3e1c6-7dc2-4567-848b-e61f35835d4d" xlink:to="loc_ifrs-full_ComputerEquipmentMember_2a80fcbd-f2e3-4302-9645-eb4862cc780d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FurnitureMember_1bf3218b-c756-42a0-adbb-14b56fc8d3f1" xlink:href="abvx-20251231.xsd#abvx_FurnitureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_8ec3e1c6-7dc2-4567-848b-e61f35835d4d" xlink:to="loc_abvx_FurnitureMember_1bf3218b-c756-42a0-adbb-14b56fc8d3f1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeAxis_31015c94-1bc7-4bec-9346-61d21ecdf749" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentTable_a9711434-40d6-4c3f-b0d1-1bd63fae70a5" xlink:to="loc_ifrs-full_RangeAxis_31015c94-1bc7-4bec-9346-61d21ecdf749" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_31015c94-1bc7-4bec-9346-61d21ecdf749_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_RangeAxis_31015c94-1bc7-4bec-9346-61d21ecdf749" xlink:to="loc_ifrs-full_RangeDomain_31015c94-1bc7-4bec-9346-61d21ecdf749_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_a030bbfd-23ff-4837-8c8c-68754dfd5ce3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_RangeAxis_31015c94-1bc7-4bec-9346-61d21ecdf749" xlink:to="loc_ifrs-full_RangeDomain_a030bbfd-23ff-4837-8c8c-68754dfd5ce3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BottomOfRangeMember_455d53a5-e8df-4434-9629-21bcdbd92cc1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BottomOfRangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_a030bbfd-23ff-4837-8c8c-68754dfd5ce3" xlink:to="loc_ifrs-full_BottomOfRangeMember_455d53a5-e8df-4434-9629-21bcdbd92cc1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TopOfRangeMember_39f9b38d-0d3e-46a3-8c44-f208e441f061" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TopOfRangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_a030bbfd-23ff-4837-8c8c-68754dfd5ce3" xlink:to="loc_ifrs-full_TopOfRangeMember_39f9b38d-0d3e-46a3-8c44-f208e441f061" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UsefulLifeMeasuredAsPeriodOfTimePropertyPlantAndEquipment_68c97c13-57c1-4fc1-a8d2-93773336f811" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UsefulLifeMeasuredAsPeriodOfTimePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentLineItems_9a14ee8e-0c9b-4c76-9b2e-9ec7e7f2e32c" xlink:to="loc_ifrs-full_UsefulLifeMeasuredAsPeriodOfTimePropertyPlantAndEquipment_68c97c13-57c1-4fc1-a8d2-93773336f811" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/SegmentinformationDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#SegmentinformationDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/SegmentinformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfGeographicalAreasLineItems_f71c2eb6-4ae0-4e54-8129-85d92ab001f7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfGeographicalAreasLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfGeographicalAreasTable_0a68bcb0-f54b-457c-8750-4669cb8c581e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfGeographicalAreasTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfGeographicalAreasLineItems_f71c2eb6-4ae0-4e54-8129-85d92ab001f7" xlink:to="loc_ifrs-full_DisclosureOfGeographicalAreasTable_0a68bcb0-f54b-457c-8750-4669cb8c581e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GeographicalAreasAxis_75667292-e3e6-498d-9bc4-324be3ac294a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GeographicalAreasAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfGeographicalAreasTable_0a68bcb0-f54b-457c-8750-4669cb8c581e" xlink:to="loc_ifrs-full_GeographicalAreasAxis_75667292-e3e6-498d-9bc4-324be3ac294a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GeographicalAreasDomain_75667292-e3e6-498d-9bc4-324be3ac294a_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GeographicalAreasDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_GeographicalAreasAxis_75667292-e3e6-498d-9bc4-324be3ac294a" xlink:to="loc_ifrs-full_GeographicalAreasDomain_75667292-e3e6-498d-9bc4-324be3ac294a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GeographicalAreasDomain_ca416f49-4d64-4d0e-9b6e-f40273a0846c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GeographicalAreasDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_GeographicalAreasAxis_75667292-e3e6-498d-9bc4-324be3ac294a" xlink:to="loc_ifrs-full_GeographicalAreasDomain_ca416f49-4d64-4d0e-9b6e-f40273a0846c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_e11111b1-10fa-489e-bd42-c26e897edae8" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_GeographicalAreasDomain_ca416f49-4d64-4d0e-9b6e-f40273a0846c" xlink:to="loc_country_US_e11111b1-10fa-489e-bd42-c26e897edae8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeAxis_c71f8361-be41-44ff-ad70-a45f525d02e8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfGeographicalAreasTable_0a68bcb0-f54b-457c-8750-4669cb8c581e" xlink:to="loc_ifrs-full_RangeAxis_c71f8361-be41-44ff-ad70-a45f525d02e8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_c71f8361-be41-44ff-ad70-a45f525d02e8_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_RangeAxis_c71f8361-be41-44ff-ad70-a45f525d02e8" xlink:to="loc_ifrs-full_RangeDomain_c71f8361-be41-44ff-ad70-a45f525d02e8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_97166769-1703-43e5-850b-6205a75a1d66" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_RangeAxis_c71f8361-be41-44ff-ad70-a45f525d02e8" xlink:to="loc_ifrs-full_RangeDomain_97166769-1703-43e5-850b-6205a75a1d66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TopOfRangeMember_bc73afa5-0da8-4ad1-a1e5-ca2cd877b941" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TopOfRangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_97166769-1703-43e5-850b-6205a75a1d66" xlink:to="loc_ifrs-full_TopOfRangeMember_bc73afa5-0da8-4ad1-a1e5-ca2cd877b941" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ContributionToGroupsLiabilitiesPercentage_3d193556-f525-4c94-ba60-0a4634272b92" xlink:href="abvx-20251231.xsd#abvx_ContributionToGroupsLiabilitiesPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfGeographicalAreasLineItems_f71c2eb6-4ae0-4e54-8129-85d92ab001f7" xlink:to="loc_abvx_ContributionToGroupsLiabilitiesPercentage_3d193556-f525-4c94-ba60-0a4634272b92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ContributionToGroupsNetProfitsLossesPercentage_c8ccff63-2288-406e-830b-f7b74e9a1b2f" xlink:href="abvx-20251231.xsd#abvx_ContributionToGroupsNetProfitsLossesPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfGeographicalAreasLineItems_f71c2eb6-4ae0-4e54-8129-85d92ab001f7" xlink:to="loc_abvx_ContributionToGroupsNetProfitsLossesPercentage_c8ccff63-2288-406e-830b-f7b74e9a1b2f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ContributionToGroupsAssetsPercentage_0b3a4e60-e7f6-4dfc-82b7-2ad76fc8d404" xlink:href="abvx-20251231.xsd#abvx_ContributionToGroupsAssetsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfGeographicalAreasLineItems_f71c2eb6-4ae0-4e54-8129-85d92ab001f7" xlink:to="loc_abvx_ContributionToGroupsAssetsPercentage_0b3a4e60-e7f6-4dfc-82b7-2ad76fc8d404" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfOperatingSegment_3e08ce28-397d-4e72-9eef-02554cb14e0a" xlink:href="abvx-20251231.xsd#abvx_NumberOfOperatingSegment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfGeographicalAreasLineItems_f71c2eb6-4ae0-4e54-8129-85d92ab001f7" xlink:to="loc_abvx_NumberOfOperatingSegment_3e08ce28-397d-4e72-9eef-02554cb14e0a" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/GoodwillandimpairmenttestDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#GoodwillandimpairmenttestDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/GoodwillandimpairmenttestDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfInformationForIndividualAssetOrCashgeneratingUnitWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesLineItems_ad67da6e-dc15-452b-a71a-def6af7158fa" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfInformationForIndividualAssetOrCashgeneratingUnitWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfInformationForIndividualAssetOrCashgeneratingUnitWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesTable_7ce07f24-7153-4d8a-a356-fa579588be69" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfInformationForIndividualAssetOrCashgeneratingUnitWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfInformationForIndividualAssetOrCashgeneratingUnitWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesLineItems_ad67da6e-dc15-452b-a71a-def6af7158fa" xlink:to="loc_ifrs-full_DisclosureOfInformationForIndividualAssetOrCashgeneratingUnitWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesTable_7ce07f24-7153-4d8a-a356-fa579588be69" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesAxis_291b2ca0-ac9f-462b-9ec4-d2e1dda6c0a3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfInformationForIndividualAssetOrCashgeneratingUnitWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesTable_7ce07f24-7153-4d8a-a356-fa579588be69" xlink:to="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesAxis_291b2ca0-ac9f-462b-9ec4-d2e1dda6c0a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain_291b2ca0-ac9f-462b-9ec4-d2e1dda6c0a3_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesAxis_291b2ca0-ac9f-462b-9ec4-d2e1dda6c0a3" xlink:to="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain_291b2ca0-ac9f-462b-9ec4-d2e1dda6c0a3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain_2c01f794-721a-4c46-95b1-ddc61f0e49b7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesAxis_291b2ca0-ac9f-462b-9ec4-d2e1dda6c0a3" xlink:to="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain_2c01f794-721a-4c46-95b1-ddc61f0e49b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WittycelSASABX196Member_91b7cd22-5ee7-4a5b-be88-290e9cff83a9" xlink:href="abvx-20251231.xsd#abvx_WittycelSASABX196Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain_2c01f794-721a-4c46-95b1-ddc61f0e49b7" xlink:to="loc_abvx_WittycelSASABX196Member_91b7cd22-5ee7-4a5b-be88-290e9cff83a9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SplicosSASABX464Member_cf042855-ca2c-47ea-924b-5c910a397ef5" xlink:href="abvx-20251231.xsd#abvx_SplicosSASABX464Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain_2c01f794-721a-4c46-95b1-ddc61f0e49b7" xlink:to="loc_abvx_SplicosSASABX464Member_cf042855-ca2c-47ea-924b-5c910a397ef5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ImpairmentLossRecognisedInProfitOrLossIntangibleAssetsAndGoodwill_29c6cfd4-bcd2-4d7a-9bbb-430de6fa6229" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ImpairmentLossRecognisedInProfitOrLossIntangibleAssetsAndGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfInformationForIndividualAssetOrCashgeneratingUnitWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesLineItems_ad67da6e-dc15-452b-a71a-def6af7158fa" xlink:to="loc_ifrs-full_ImpairmentLossRecognisedInProfitOrLossIntangibleAssetsAndGoodwill_29c6cfd4-bcd2-4d7a-9bbb-430de6fa6229" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ImpairmentLossRecognisedInProfitOrLossGoodwill_390420e1-ebb5-403e-a5b6-7684ebfe94dd" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ImpairmentLossRecognisedInProfitOrLossGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfInformationForIndividualAssetOrCashgeneratingUnitWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesLineItems_ad67da6e-dc15-452b-a71a-def6af7158fa" xlink:to="loc_ifrs-full_ImpairmentLossRecognisedInProfitOrLossGoodwill_390420e1-ebb5-403e-a5b6-7684ebfe94dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ImpairmentLossRecognisedInProfitOrLossIntangibleAssetsOtherThanGoodwill_61668205-f84a-4d2f-9d5b-4d6e491cd8e1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ImpairmentLossRecognisedInProfitOrLossIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfInformationForIndividualAssetOrCashgeneratingUnitWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesLineItems_ad67da6e-dc15-452b-a71a-def6af7158fa" xlink:to="loc_ifrs-full_ImpairmentLossRecognisedInProfitOrLossIntangibleAssetsOtherThanGoodwill_61668205-f84a-4d2f-9d5b-4d6e491cd8e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_Goodwill_18ca5e2f-5e26-4846-83e7-3dbbf4ff037a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfInformationForIndividualAssetOrCashgeneratingUnitWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesLineItems_ad67da6e-dc15-452b-a71a-def6af7158fa" xlink:to="loc_ifrs-full_Goodwill_18ca5e2f-5e26-4846-83e7-3dbbf4ff037a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DescriptionOfDiscountRatesAppliedToCashFlowProjections_d9a131eb-661c-401e-b05a-bbea18c85042" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DescriptionOfDiscountRatesAppliedToCashFlowProjections"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfInformationForIndividualAssetOrCashgeneratingUnitWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesLineItems_ad67da6e-dc15-452b-a71a-def6af7158fa" xlink:to="loc_ifrs-full_DescriptionOfDiscountRatesAppliedToCashFlowProjections_d9a131eb-661c-401e-b05a-bbea18c85042" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/IntangibleassetsNarrativeDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#IntangibleassetsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/IntangibleassetsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfIntangibleAssetsLineItems_c34c5875-f0c5-410c-b869-f38dbd456720" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfIntangibleAssetsTable_45262169-2d94-4001-bcb2-4dc85757dc4f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsLineItems_c34c5875-f0c5-410c-b869-f38dbd456720" xlink:to="loc_ifrs-full_DisclosureOfIntangibleAssetsTable_45262169-2d94-4001-bcb2-4dc85757dc4f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesAxis_395b4aea-6b13-4e2e-906a-b3d771928bf9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsTable_45262169-2d94-4001-bcb2-4dc85757dc4f" xlink:to="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesAxis_395b4aea-6b13-4e2e-906a-b3d771928bf9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain_395b4aea-6b13-4e2e-906a-b3d771928bf9_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesAxis_395b4aea-6b13-4e2e-906a-b3d771928bf9" xlink:to="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain_395b4aea-6b13-4e2e-906a-b3d771928bf9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain_81cd9d1a-ec6c-4bda-a7ea-4dc16a59ab46" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesAxis_395b4aea-6b13-4e2e-906a-b3d771928bf9" xlink:to="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain_81cd9d1a-ec6c-4bda-a7ea-4dc16a59ab46" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WittycelSASABX196Member_96049b93-2ddc-478c-a8b8-eea114c3dc0a" xlink:href="abvx-20251231.xsd#abvx_WittycelSASABX196Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_IndividualAssetsOrCashgeneratingUnitsWithSignificantAmountOfGoodwillOrIntangibleAssetsWithIndefiniteUsefulLivesDomain_81cd9d1a-ec6c-4bda-a7ea-4dc16a59ab46" xlink:to="loc_abvx_WittycelSASABX196Member_96049b93-2ddc-478c-a8b8-eea114c3dc0a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PrincipalAgreementsAxis_0290f461-e78b-4104-8909-29cf81e34b10" xlink:href="abvx-20251231.xsd#abvx_PrincipalAgreementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsTable_45262169-2d94-4001-bcb2-4dc85757dc4f" xlink:to="loc_abvx_PrincipalAgreementsAxis_0290f461-e78b-4104-8909-29cf81e34b10" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PrincipalAgreementsDomain_0290f461-e78b-4104-8909-29cf81e34b10_default" xlink:href="abvx-20251231.xsd#abvx_PrincipalAgreementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_PrincipalAgreementsAxis_0290f461-e78b-4104-8909-29cf81e34b10" xlink:to="loc_abvx_PrincipalAgreementsDomain_0290f461-e78b-4104-8909-29cf81e34b10_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PrincipalAgreementsDomain_ffd8649a-8948-41dc-a0d5-6958057aa0f4" xlink:href="abvx-20251231.xsd#abvx_PrincipalAgreementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_PrincipalAgreementsAxis_0290f461-e78b-4104-8909-29cf81e34b10" xlink:to="loc_abvx_PrincipalAgreementsDomain_ffd8649a-8948-41dc-a0d5-6958057aa0f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExclusiveLicensingContractWithTheScrippsResearchInstituteUniversityOfChicagoAndBrighamYoungUniversityMember_90fca1cd-a9e5-4082-8adb-4d056e106d40" xlink:href="abvx-20251231.xsd#abvx_ExclusiveLicensingContractWithTheScrippsResearchInstituteUniversityOfChicagoAndBrighamYoungUniversityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_PrincipalAgreementsDomain_ffd8649a-8948-41dc-a0d5-6958057aa0f4" xlink:to="loc_abvx_ExclusiveLicensingContractWithTheScrippsResearchInstituteUniversityOfChicagoAndBrighamYoungUniversityMember_90fca1cd-a9e5-4082-8adb-4d056e106d40" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExclusiveLicensingAgreementWithCNRSUniversityOfMontpellierAndInstitutCurieMember_fddab8b1-338c-4372-a1f1-1dd4580e7ff7" xlink:href="abvx-20251231.xsd#abvx_ExclusiveLicensingAgreementWithCNRSUniversityOfMontpellierAndInstitutCurieMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_PrincipalAgreementsDomain_ffd8649a-8948-41dc-a0d5-6958057aa0f4" xlink:to="loc_abvx_ExclusiveLicensingAgreementWithCNRSUniversityOfMontpellierAndInstitutCurieMember_fddab8b1-338c-4372-a1f1-1dd4580e7ff7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AssetsAcquisitionsAxis_5e9b01eb-45f8-4afd-8cae-43c85efa5a19" xlink:href="abvx-20251231.xsd#abvx_AssetsAcquisitionsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsTable_45262169-2d94-4001-bcb2-4dc85757dc4f" xlink:to="loc_abvx_AssetsAcquisitionsAxis_5e9b01eb-45f8-4afd-8cae-43c85efa5a19" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AssetsAcquisitionsDomain_5e9b01eb-45f8-4afd-8cae-43c85efa5a19_default" xlink:href="abvx-20251231.xsd#abvx_AssetsAcquisitionsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_AssetsAcquisitionsAxis_5e9b01eb-45f8-4afd-8cae-43c85efa5a19" xlink:to="loc_abvx_AssetsAcquisitionsDomain_5e9b01eb-45f8-4afd-8cae-43c85efa5a19_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AssetsAcquisitionsDomain_726b1c97-3830-410b-a88b-3f6ebc2087ee" xlink:href="abvx-20251231.xsd#abvx_AssetsAcquisitionsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_AssetsAcquisitionsAxis_5e9b01eb-45f8-4afd-8cae-43c85efa5a19" xlink:to="loc_abvx_AssetsAcquisitionsDomain_726b1c97-3830-410b-a88b-3f6ebc2087ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ProsynergiaMember_100463fc-1573-4373-bbe2-4cec7c5484c0" xlink:href="abvx-20251231.xsd#abvx_ProsynergiaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_AssetsAcquisitionsDomain_726b1c97-3830-410b-a88b-3f6ebc2087ee" xlink:to="loc_abvx_ProsynergiaMember_100463fc-1573-4373-bbe2-4cec7c5484c0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CollaborationAgreementsDevelopmentMilestonePaymentINDApproval_ffbc8671-5dce-47f4-91df-3412c3949170" xlink:href="abvx-20251231.xsd#abvx_CollaborationAgreementsDevelopmentMilestonePaymentINDApproval"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsLineItems_c34c5875-f0c5-410c-b869-f38dbd456720" xlink:to="loc_abvx_CollaborationAgreementsDevelopmentMilestonePaymentINDApproval_ffbc8671-5dce-47f4-91df-3412c3949170" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IntangibleAssetsWithIndefiniteUsefulLife_d53f55ea-d771-4bb0-8ce5-7490b101be20" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IntangibleAssetsWithIndefiniteUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsLineItems_c34c5875-f0c5-410c-b869-f38dbd456720" xlink:to="loc_ifrs-full_IntangibleAssetsWithIndefiniteUsefulLife_d53f55ea-d771-4bb0-8ce5-7490b101be20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ImpairmentLossRecognisedInProfitOrLossIntangibleAssetsOtherThanGoodwill_8eafd51c-14c8-4b28-9ddd-568f2a51f9a3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ImpairmentLossRecognisedInProfitOrLossIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsLineItems_c34c5875-f0c5-410c-b869-f38dbd456720" xlink:to="loc_ifrs-full_ImpairmentLossRecognisedInProfitOrLossIntangibleAssetsOtherThanGoodwill_8eafd51c-14c8-4b28-9ddd-568f2a51f9a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CollaborationAgreementsDevelopmentMilestonePaymentPhase2_a5e433a1-1a87-4429-bf48-813281cc84e4" xlink:href="abvx-20251231.xsd#abvx_CollaborationAgreementsDevelopmentMilestonePaymentPhase2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsLineItems_c34c5875-f0c5-410c-b869-f38dbd456720" xlink:to="loc_abvx_CollaborationAgreementsDevelopmentMilestonePaymentPhase2_a5e433a1-1a87-4429-bf48-813281cc84e4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TechnologyBasedIntangibleAssetsAssetsAcquisitions_0c95c135-aca9-432f-a6d6-7ca4cde97a46" xlink:href="abvx-20251231.xsd#abvx_TechnologyBasedIntangibleAssetsAssetsAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsLineItems_c34c5875-f0c5-410c-b869-f38dbd456720" xlink:to="loc_abvx_TechnologyBasedIntangibleAssetsAssetsAcquisitions_0c95c135-aca9-432f-a6d6-7ca4cde97a46" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/IntangibleassetsDisclosureofreconciliationofintangibleassetsDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#IntangibleassetsDisclosureofreconciliationofintangibleassetsDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/IntangibleassetsDisclosureofreconciliationofintangibleassetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfIntangibleAssetsLineItems_2b328002-ff56-48ff-820b-14f1cf8ea1b3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfIntangibleAssetsTable_9dddb4ec-a016-4402-85bd-fbd0e40d9355" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsLineItems_2b328002-ff56-48ff-820b-14f1cf8ea1b3" xlink:to="loc_ifrs-full_DisclosureOfIntangibleAssetsTable_9dddb4ec-a016-4402-85bd-fbd0e40d9355" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_58ecf613-e94d-4ef1-99ff-ca1477076fac" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsTable_9dddb4ec-a016-4402-85bd-fbd0e40d9355" xlink:to="loc_ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_58ecf613-e94d-4ef1-99ff-ca1477076fac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CarryingAmountMember_58ecf613-e94d-4ef1-99ff-ca1477076fac_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_58ecf613-e94d-4ef1-99ff-ca1477076fac" xlink:to="loc_ifrs-full_CarryingAmountMember_58ecf613-e94d-4ef1-99ff-ca1477076fac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CarryingAmountMember_256e4d0c-8163-417f-91fd-5cc8ca23359b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_58ecf613-e94d-4ef1-99ff-ca1477076fac" xlink:to="loc_ifrs-full_CarryingAmountMember_256e4d0c-8163-417f-91fd-5cc8ca23359b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GrossCarryingAmountMember_b0256efb-6ae9-4283-bdb1-41623c290b0c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GrossCarryingAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_CarryingAmountMember_256e4d0c-8163-417f-91fd-5cc8ca23359b" xlink:to="loc_ifrs-full_GrossCarryingAmountMember_b0256efb-6ae9-4283-bdb1-41623c290b0c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AccumulatedDepreciationAmortisationAndImpairmentMember_8ba98db0-db2d-4e0f-b67b-c8ca07a760da" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AccumulatedDepreciationAmortisationAndImpairmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_CarryingAmountMember_256e4d0c-8163-417f-91fd-5cc8ca23359b" xlink:to="loc_ifrs-full_AccumulatedDepreciationAmortisationAndImpairmentMember_8ba98db0-db2d-4e0f-b67b-c8ca07a760da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillAxis_ee3d7914-6651-4f24-ac0b-1cf4a7c2a8f7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsTable_9dddb4ec-a016-4402-85bd-fbd0e40d9355" xlink:to="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillAxis_ee3d7914-6651-4f24-ac0b-1cf4a7c2a8f7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain_ee3d7914-6651-4f24-ac0b-1cf4a7c2a8f7_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillAxis_ee3d7914-6651-4f24-ac0b-1cf4a7c2a8f7" xlink:to="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain_ee3d7914-6651-4f24-ac0b-1cf4a7c2a8f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain_013f4f13-c0e7-4563-be7e-ac0c80d6eb71" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillAxis_ee3d7914-6651-4f24-ac0b-1cf4a7c2a8f7" xlink:to="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain_013f4f13-c0e7-4563-be7e-ac0c80d6eb71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LicencesMember_428fd6b0-0733-4a24-8c84-cc57897cada2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LicencesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain_013f4f13-c0e7-4563-be7e-ac0c80d6eb71" xlink:to="loc_ifrs-full_LicencesMember_428fd6b0-0733-4a24-8c84-cc57897cada2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ComputerSoftwareMember_a8e76dc5-4d1d-4ce6-90d3-1bf3f809c9b5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComputerSoftwareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain_013f4f13-c0e7-4563-be7e-ac0c80d6eb71" xlink:to="loc_ifrs-full_ComputerSoftwareMember_a8e76dc5-4d1d-4ce6-90d3-1bf3f809c9b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CopyrightsPatentsAndOtherIndustrialPropertyRightsServiceAndOperatingRightsMember_d6755779-c8a6-4f8f-8973-305fcfbe73f3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CopyrightsPatentsAndOtherIndustrialPropertyRightsServiceAndOperatingRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillDomain_013f4f13-c0e7-4563-be7e-ac0c80d6eb71" xlink:to="loc_ifrs-full_CopyrightsPatentsAndOtherIndustrialPropertyRightsServiceAndOperatingRightsMember_d6755779-c8a6-4f8f-8973-305fcfbe73f3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ReconciliationOfChangesInIntangibleAssetsOtherThanGoodwillAbstract_9216e72d-1f7c-4454-af69-a3b14d63be1d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ReconciliationOfChangesInIntangibleAssetsOtherThanGoodwillAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfIntangibleAssetsLineItems_2b328002-ff56-48ff-820b-14f1cf8ea1b3" xlink:to="loc_ifrs-full_ReconciliationOfChangesInIntangibleAssetsOtherThanGoodwillAbstract_9216e72d-1f7c-4454-af69-a3b14d63be1d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IntangibleAssetsOtherThanGoodwill_e2a0cdb9-214b-4be3-bff4-07a1fdefa283" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ReconciliationOfChangesInIntangibleAssetsOtherThanGoodwillAbstract_9216e72d-1f7c-4454-af69-a3b14d63be1d" xlink:to="loc_ifrs-full_IntangibleAssetsOtherThanGoodwill_e2a0cdb9-214b-4be3-bff4-07a1fdefa283" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AdditionsOtherThanThroughBusinessCombinationsIntangibleAssetsOtherThanGoodwill_2bf9776c-efb7-41f6-a143-cf3a501c82a6" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AdditionsOtherThanThroughBusinessCombinationsIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ReconciliationOfChangesInIntangibleAssetsOtherThanGoodwillAbstract_9216e72d-1f7c-4454-af69-a3b14d63be1d" xlink:to="loc_ifrs-full_AdditionsOtherThanThroughBusinessCombinationsIntangibleAssetsOtherThanGoodwill_2bf9776c-efb7-41f6-a143-cf3a501c82a6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AmortisationIntangibleAssetsOtherThanGoodwill_94b8b45f-e34e-4f4b-a5e8-a6569347cdd9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AmortisationIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ReconciliationOfChangesInIntangibleAssetsOtherThanGoodwillAbstract_9216e72d-1f7c-4454-af69-a3b14d63be1d" xlink:to="loc_ifrs-full_AmortisationIntangibleAssetsOtherThanGoodwill_94b8b45f-e34e-4f4b-a5e8-a6569347cdd9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IntangibleAssetsOtherThanGoodwill_72fc40f6-6d80-4d83-86a3-133023fa630c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IntangibleAssetsOtherThanGoodwill"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/PropertyplantandequipmentDisclosureofreconciliationofpropertyplantandequipmentDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#PropertyplantandequipmentDisclosureofreconciliationofpropertyplantandequipmentDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/PropertyplantandequipmentDisclosureofreconciliationofpropertyplantandequipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentLineItems_7152fb62-7ec2-44c5-a7f7-0aacfe877d3f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfPropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentTable_4a773fee-a2bb-4eb8-8a4e-73054c5f62d2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentLineItems_7152fb62-7ec2-44c5-a7f7-0aacfe877d3f" xlink:to="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentTable_4a773fee-a2bb-4eb8-8a4e-73054c5f62d2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_fc04495c-5dad-4a83-bc92-d04ee0d96365" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentTable_4a773fee-a2bb-4eb8-8a4e-73054c5f62d2" xlink:to="loc_ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_fc04495c-5dad-4a83-bc92-d04ee0d96365" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CarryingAmountMember_fc04495c-5dad-4a83-bc92-d04ee0d96365_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_fc04495c-5dad-4a83-bc92-d04ee0d96365" xlink:to="loc_ifrs-full_CarryingAmountMember_fc04495c-5dad-4a83-bc92-d04ee0d96365_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CarryingAmountMember_edd4f8cf-d5e4-466f-b12c-2d3225384740" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_fc04495c-5dad-4a83-bc92-d04ee0d96365" xlink:to="loc_ifrs-full_CarryingAmountMember_edd4f8cf-d5e4-466f-b12c-2d3225384740" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GrossCarryingAmountMember_13e98174-83a8-45e9-9657-49e52b508a99" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GrossCarryingAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_CarryingAmountMember_edd4f8cf-d5e4-466f-b12c-2d3225384740" xlink:to="loc_ifrs-full_GrossCarryingAmountMember_13e98174-83a8-45e9-9657-49e52b508a99" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AccumulatedDepreciationAndAmortisationMember_71b6b4e4-86a2-48a8-95f9-0a0804bb61e7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AccumulatedDepreciationAndAmortisationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_CarryingAmountMember_edd4f8cf-d5e4-466f-b12c-2d3225384740" xlink:to="loc_ifrs-full_AccumulatedDepreciationAndAmortisationMember_71b6b4e4-86a2-48a8-95f9-0a0804bb61e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis_03fd40e3-8bb2-4904-81d7-ca4146cf5b5a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentTable_4a773fee-a2bb-4eb8-8a4e-73054c5f62d2" xlink:to="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis_03fd40e3-8bb2-4904-81d7-ca4146cf5b5a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_03fd40e3-8bb2-4904-81d7-ca4146cf5b5a_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis_03fd40e3-8bb2-4904-81d7-ca4146cf5b5a" xlink:to="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_03fd40e3-8bb2-4904-81d7-ca4146cf5b5a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_0ae40ba1-1397-48a5-9957-8d9f6241106a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis_03fd40e3-8bb2-4904-81d7-ca4146cf5b5a" xlink:to="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_0ae40ba1-1397-48a5-9957-8d9f6241106a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BuildingsMember_1c5bd328-8425-443d-95fa-df76e3ce57ba" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BuildingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_0ae40ba1-1397-48a5-9957-8d9f6241106a" xlink:to="loc_ifrs-full_BuildingsMember_1c5bd328-8425-443d-95fa-df76e3ce57ba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OfficeEquipmentMember_019bf9cc-506f-72d9-a9fa-f2872638d9b0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OfficeEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_0ae40ba1-1397-48a5-9957-8d9f6241106a" xlink:to="loc_ifrs-full_OfficeEquipmentMember_019bf9cc-506f-72d9-a9fa-f2872638d9b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FurnitureAndComputerEquipmentMember_59c71fef-fb02-4bfd-86bb-ce3f2b0ec6b5" xlink:href="abvx-20251231.xsd#abvx_FurnitureAndComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfPropertyPlantAndEquipmentDomain_0ae40ba1-1397-48a5-9957-8d9f6241106a" xlink:to="loc_abvx_FurnitureAndComputerEquipmentMember_59c71fef-fb02-4bfd-86bb-ce3f2b0ec6b5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssetsAxis_4d42dd46-ce68-46a1-85f0-85b34701623e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssetsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentTable_4a773fee-a2bb-4eb8-8a4e-73054c5f62d2" xlink:to="loc_ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssetsAxis_4d42dd46-ce68-46a1-85f0-85b34701623e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssetsDomain_4d42dd46-ce68-46a1-85f0-85b34701623e_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssetsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssetsAxis_4d42dd46-ce68-46a1-85f0-85b34701623e" xlink:to="loc_ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssetsDomain_4d42dd46-ce68-46a1-85f0-85b34701623e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssetsDomain_5c73695b-b942-4b6d-a62c-b4ca3d380771" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssetsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssetsAxis_4d42dd46-ce68-46a1-85f0-85b34701623e" xlink:to="loc_ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssetsDomain_5c73695b-b942-4b6d-a62c-b4ca3d380771" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PropertyPlantAndEquipmentMember_019bf9cf-a8a5-755f-99bf-38d49debd4c7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PropertyPlantAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssetsDomain_5c73695b-b942-4b6d-a62c-b4ca3d380771" xlink:to="loc_ifrs-full_PropertyPlantAndEquipmentMember_019bf9cf-a8a5-755f-99bf-38d49debd4c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RightofuseAssetsMember_dbc0249b-d617-4f78-8505-f959a384a0c0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RightofuseAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssetsDomain_5c73695b-b942-4b6d-a62c-b4ca3d380771" xlink:to="loc_ifrs-full_RightofuseAssetsMember_dbc0249b-d617-4f78-8505-f959a384a0c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ReconciliationOfChangesInPropertyPlantAndEquipmentAbstract_41788080-0be5-413d-b967-609226b88b2f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ReconciliationOfChangesInPropertyPlantAndEquipmentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfPropertyPlantAndEquipmentLineItems_7152fb62-7ec2-44c5-a7f7-0aacfe877d3f" xlink:to="loc_ifrs-full_ReconciliationOfChangesInPropertyPlantAndEquipmentAbstract_41788080-0be5-413d-b967-609226b88b2f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssets_f6c16bb2-e86c-432d-a8f0-6d9763b844fa" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ReconciliationOfChangesInPropertyPlantAndEquipmentAbstract_41788080-0be5-413d-b967-609226b88b2f" xlink:to="loc_ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssets_f6c16bb2-e86c-432d-a8f0-6d9763b844fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AdditionsOtherThanThroughBusinessCombinationsPropertyPlantAndEquipmentIncludingRightofuseAssets_e36731a8-afc8-4c15-b8d3-d778db8fe1ff" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AdditionsOtherThanThroughBusinessCombinationsPropertyPlantAndEquipmentIncludingRightofuseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ReconciliationOfChangesInPropertyPlantAndEquipmentAbstract_41788080-0be5-413d-b967-609226b88b2f" xlink:to="loc_ifrs-full_AdditionsOtherThanThroughBusinessCombinationsPropertyPlantAndEquipmentIncludingRightofuseAssets_e36731a8-afc8-4c15-b8d3-d778db8fe1ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DepreciationPropertyPlantAndEquipmentIncludingRightofuseAssets_d1099089-5263-4b32-8e02-9f8d3c262827" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DepreciationPropertyPlantAndEquipmentIncludingRightofuseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ReconciliationOfChangesInPropertyPlantAndEquipmentAbstract_41788080-0be5-413d-b967-609226b88b2f" xlink:to="loc_ifrs-full_DepreciationPropertyPlantAndEquipmentIncludingRightofuseAssets_d1099089-5263-4b32-8e02-9f8d3c262827" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisposalsPropertyPlantAndEquipmentIncludingRightofuseAssets_bb9c32d2-c390-4f3a-ac91-2cf6a45b8aea" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisposalsPropertyPlantAndEquipmentIncludingRightofuseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ReconciliationOfChangesInPropertyPlantAndEquipmentAbstract_41788080-0be5-413d-b967-609226b88b2f" xlink:to="loc_ifrs-full_DisposalsPropertyPlantAndEquipmentIncludingRightofuseAssets_bb9c32d2-c390-4f3a-ac91-2cf6a45b8aea" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughNetExchangeDifferencesPropertyPlantAndEquipmentIncludingRightofuseAssets_5b780b77-defb-4387-847e-208f359b7c7a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughNetExchangeDifferencesPropertyPlantAndEquipmentIncludingRightofuseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ReconciliationOfChangesInPropertyPlantAndEquipmentAbstract_41788080-0be5-413d-b967-609226b88b2f" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughNetExchangeDifferencesPropertyPlantAndEquipmentIncludingRightofuseAssets_5b780b77-defb-4387-847e-208f359b7c7a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssets_eeeed366-6400-4baa-907a-2838807d2be7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PropertyPlantAndEquipmentIncludingRightofuseAssets"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/PropertyplantandequipmentNarrativeDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#PropertyplantandequipmentNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/PropertyplantandequipmentNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfQuantitativeInformationAboutRightofuseAssetsLineItems_35a4ee22-cbe8-47f3-a69f-d7931ad28cc0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfQuantitativeInformationAboutRightofuseAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfQuantitativeInformationAboutRightofuseAssetsTable_08aee887-2ab3-4357-b034-3f2bdecf5feb" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfQuantitativeInformationAboutRightofuseAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfQuantitativeInformationAboutRightofuseAssetsLineItems_35a4ee22-cbe8-47f3-a69f-d7931ad28cc0" xlink:to="loc_ifrs-full_DisclosureOfQuantitativeInformationAboutRightofuseAssetsTable_08aee887-2ab3-4357-b034-3f2bdecf5feb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfContractsAxis_daf30111-89c6-4824-a6af-498c8b0c2bb0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfContractsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfQuantitativeInformationAboutRightofuseAssetsTable_08aee887-2ab3-4357-b034-3f2bdecf5feb" xlink:to="loc_ifrs-full_TypesOfContractsAxis_daf30111-89c6-4824-a6af-498c8b0c2bb0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfContractsDomain_daf30111-89c6-4824-a6af-498c8b0c2bb0_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfContractsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfContractsAxis_daf30111-89c6-4824-a6af-498c8b0c2bb0" xlink:to="loc_ifrs-full_TypesOfContractsDomain_daf30111-89c6-4824-a6af-498c8b0c2bb0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfContractsDomain_88778690-4275-4314-b1a9-be9238e60c25" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfContractsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfContractsAxis_daf30111-89c6-4824-a6af-498c8b0c2bb0" xlink:to="loc_ifrs-full_TypesOfContractsDomain_88778690-4275-4314-b1a9-be9238e60c25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_LeaseFacilitiesParisMember_114f8aff-80ac-4470-899f-fb9bebdd3da9" xlink:href="abvx-20251231.xsd#abvx_LeaseFacilitiesParisMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfContractsDomain_88778690-4275-4314-b1a9-be9238e60c25" xlink:to="loc_abvx_LeaseFacilitiesParisMember_114f8aff-80ac-4470-899f-fb9bebdd3da9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfAssetsAxis_566b6da6-2bf9-4383-8f73-d4f3862922e4" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfAssetsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfQuantitativeInformationAboutRightofuseAssetsTable_08aee887-2ab3-4357-b034-3f2bdecf5feb" xlink:to="loc_ifrs-full_ClassesOfAssetsAxis_566b6da6-2bf9-4383-8f73-d4f3862922e4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfAssetsDomain_566b6da6-2bf9-4383-8f73-d4f3862922e4_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfAssetsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfAssetsAxis_566b6da6-2bf9-4383-8f73-d4f3862922e4" xlink:to="loc_ifrs-full_ClassesOfAssetsDomain_566b6da6-2bf9-4383-8f73-d4f3862922e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfAssetsDomain_752cadfa-34a6-4f76-9d43-3aedc2cc6b6b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfAssetsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfAssetsAxis_566b6da6-2bf9-4383-8f73-d4f3862922e4" xlink:to="loc_ifrs-full_ClassesOfAssetsDomain_752cadfa-34a6-4f76-9d43-3aedc2cc6b6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BuildingsMember_f99aaf2b-64db-4855-bb50-6efddde1b200" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BuildingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfAssetsDomain_752cadfa-34a6-4f76-9d43-3aedc2cc6b6b" xlink:to="loc_ifrs-full_BuildingsMember_f99aaf2b-64db-4855-bb50-6efddde1b200" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RightofuseAssets_8126817a-e5ac-4aea-9942-1752729e2ba7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RightofuseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfQuantitativeInformationAboutRightofuseAssetsLineItems_35a4ee22-cbe8-47f3-a69f-d7931ad28cc0" xlink:to="loc_ifrs-full_RightofuseAssets_8126817a-e5ac-4aea-9942-1752729e2ba7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DecreaseThroughReassessmentOfLeaseTermRightOfUseAssets_cdfabcc5-8f86-4974-a7e7-fc4b5ca8e57c" xlink:href="abvx-20251231.xsd#abvx_DecreaseThroughReassessmentOfLeaseTermRightOfUseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfQuantitativeInformationAboutRightofuseAssetsLineItems_35a4ee22-cbe8-47f3-a69f-d7931ad28cc0" xlink:to="loc_abvx_DecreaseThroughReassessmentOfLeaseTermRightOfUseAssets_cdfabcc5-8f86-4974-a7e7-fc4b5ca8e57c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/OtherfinancialassetsNarrativeDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#OtherfinancialassetsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/OtherfinancialassetsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfFinancialAssetsLineItems_0cc33eb0-c14a-43bd-b056-8af83102661f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfFinancialAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfFinancialAssetsTable_69b1b92c-7f1d-4521-bb64-5a1d0d5010fe" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfFinancialAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfFinancialAssetsLineItems_0cc33eb0-c14a-43bd-b056-8af83102661f" xlink:to="loc_ifrs-full_DisclosureOfFinancialAssetsTable_69b1b92c-7f1d-4521-bb64-5a1d0d5010fe" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeAxis_5f9b5b2b-d1f7-468c-be6b-c4ea4684b74b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfFinancialAssetsTable_69b1b92c-7f1d-4521-bb64-5a1d0d5010fe" xlink:to="loc_ifrs-full_RangeAxis_5f9b5b2b-d1f7-468c-be6b-c4ea4684b74b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_5f9b5b2b-d1f7-468c-be6b-c4ea4684b74b_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_RangeAxis_5f9b5b2b-d1f7-468c-be6b-c4ea4684b74b" xlink:to="loc_ifrs-full_RangeDomain_5f9b5b2b-d1f7-468c-be6b-c4ea4684b74b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_b2e4cb60-6f1e-42a5-88fb-5031c364b9b3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_RangeAxis_5f9b5b2b-d1f7-468c-be6b-c4ea4684b74b" xlink:to="loc_ifrs-full_RangeDomain_b2e4cb60-6f1e-42a5-88fb-5031c364b9b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BottomOfRangeMember_cba50796-5cf0-4466-aca7-e67d78555d93" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BottomOfRangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_b2e4cb60-6f1e-42a5-88fb-5031c364b9b3" xlink:to="loc_ifrs-full_BottomOfRangeMember_cba50796-5cf0-4466-aca7-e67d78555d93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TopOfRangeMember_a65283db-6d71-4512-9a92-181696bba450" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TopOfRangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_b2e4cb60-6f1e-42a5-88fb-5031c364b9b3" xlink:to="loc_ifrs-full_TopOfRangeMember_a65283db-6d71-4512-9a92-181696bba450" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NonCurrentAdvancesToCROContractsUndiscountedAmount_019c524e-b46b-78c9-b595-00fa1e57fdea" xlink:href="abvx-20251231.xsd#abvx_NonCurrentAdvancesToCROContractsUndiscountedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfFinancialAssetsLineItems_0cc33eb0-c14a-43bd-b056-8af83102661f" xlink:to="loc_abvx_NonCurrentAdvancesToCROContractsUndiscountedAmount_019c524e-b46b-78c9-b595-00fa1e57fdea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DiscountRateAppliedToLongTermAdvances_e6c6270c-ba89-4748-9812-f5c16bf00974" xlink:href="abvx-20251231.xsd#abvx_DiscountRateAppliedToLongTermAdvances"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfFinancialAssetsLineItems_0cc33eb0-c14a-43bd-b056-8af83102661f" xlink:to="loc_abvx_DiscountRateAppliedToLongTermAdvances_e6c6270c-ba89-4748-9812-f5c16bf00974" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PaymentsForAdvancesMadeToContractResearchOrganizationsUndiscountedAmount_6986fa31-f4eb-4a18-bab5-6ba6ab864bc1" xlink:href="abvx-20251231.xsd#abvx_PaymentsForAdvancesMadeToContractResearchOrganizationsUndiscountedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfFinancialAssetsLineItems_0cc33eb0-c14a-43bd-b056-8af83102661f" xlink:to="loc_abvx_PaymentsForAdvancesMadeToContractResearchOrganizationsUndiscountedAmount_6986fa31-f4eb-4a18-bab5-6ba6ab864bc1" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/OtherreceivablesandotherassetsNarrativeDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#OtherreceivablesandotherassetsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/OtherreceivablesandotherassetsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfOtherReceivablesAndOtherAssetsLineItems_a10b0bc7-6763-48f3-b274-5caeb6dabfef" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfOtherReceivablesAndOtherAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfOtherReceivablesAndOtherAssetsTable_5c5aad94-551e-4f9e-9a94-ff9ef4e2b063" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfOtherReceivablesAndOtherAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_abvx_DisclosureOfOtherReceivablesAndOtherAssetsLineItems_a10b0bc7-6763-48f3-b274-5caeb6dabfef" xlink:to="loc_abvx_DisclosureOfOtherReceivablesAndOtherAssetsTable_5c5aad94-551e-4f9e-9a94-ff9ef4e2b063" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_b93ba26b-e70f-4cd9-a5b1-a5d87d3de075" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfOtherReceivablesAndOtherAssetsTable_5c5aad94-551e-4f9e-9a94-ff9ef4e2b063" xlink:to="loc_ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_b93ba26b-e70f-4cd9-a5b1-a5d87d3de075" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CarryingAmountMember_b93ba26b-e70f-4cd9-a5b1-a5d87d3de075_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_b93ba26b-e70f-4cd9-a5b1-a5d87d3de075" xlink:to="loc_ifrs-full_CarryingAmountMember_b93ba26b-e70f-4cd9-a5b1-a5d87d3de075_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CarryingAmountMember_833fccbc-8669-405e-a07c-f2c483941600" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_b93ba26b-e70f-4cd9-a5b1-a5d87d3de075" xlink:to="loc_ifrs-full_CarryingAmountMember_833fccbc-8669-405e-a07c-f2c483941600" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DeferredFinancingCostsNettingMember_3e25dc6b-48ae-4fb8-b80a-6a6d13f835d7" xlink:href="abvx-20251231.xsd#abvx_DeferredFinancingCostsNettingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_CarryingAmountMember_833fccbc-8669-405e-a07c-f2c483941600" xlink:to="loc_abvx_DeferredFinancingCostsNettingMember_3e25dc6b-48ae-4fb8-b80a-6a6d13f835d7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_b071abbf-d0fa-4f99-942c-54566e18526c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfOtherReceivablesAndOtherAssetsTable_5c5aad94-551e-4f9e-9a94-ff9ef4e2b063" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_b071abbf-d0fa-4f99-942c-54566e18526c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_b071abbf-d0fa-4f99-942c-54566e18526c_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_b071abbf-d0fa-4f99-942c-54566e18526c" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_b071abbf-d0fa-4f99-942c-54566e18526c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_f260e9ef-cec9-4dcc-858b-7833a7efcc00" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_b071abbf-d0fa-4f99-942c-54566e18526c" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_f260e9ef-cec9-4dcc-858b-7833a7efcc00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheBMember_735eb06a-4e28-4578-bb1c-c19d659b6822" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_f260e9ef-cec9-4dcc-858b-7833a7efcc00" xlink:to="loc_abvx_KreosClaretFinancingTrancheBMember_735eb06a-4e28-4578-bb1c-c19d659b6822" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ProceedsFromResearchTaxCredit_504ee738-644c-481c-a49d-e1c743e578f0" xlink:href="abvx-20251231.xsd#abvx_ProceedsFromResearchTaxCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOtherReceivablesAndOtherAssetsLineItems_a10b0bc7-6763-48f3-b274-5caeb6dabfef" xlink:to="loc_abvx_ProceedsFromResearchTaxCredit_504ee738-644c-481c-a49d-e1c743e578f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CurrentResearchTaxCreditReceivables_0e229e10-28b1-49af-b5c7-199566907aa9" xlink:href="abvx-20251231.xsd#abvx_CurrentResearchTaxCreditReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOtherReceivablesAndOtherAssetsLineItems_a10b0bc7-6763-48f3-b274-5caeb6dabfef" xlink:to="loc_abvx_CurrentResearchTaxCreditReceivables_0e229e10-28b1-49af-b5c7-199566907aa9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CurrentPrepaidExpensesRelatedToCRO_80bbd16b-062b-43fa-8a9d-495ed5ad0da4" xlink:href="abvx-20251231.xsd#abvx_CurrentPrepaidExpensesRelatedToCRO"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOtherReceivablesAndOtherAssetsLineItems_a10b0bc7-6763-48f3-b274-5caeb6dabfef" xlink:to="loc_abvx_CurrentPrepaidExpensesRelatedToCRO_80bbd16b-062b-43fa-8a9d-495ed5ad0da4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_Borrowings_c3185b92-2916-47a4-97fc-8b69c439a376" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Borrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOtherReceivablesAndOtherAssetsLineItems_a10b0bc7-6763-48f3-b274-5caeb6dabfef" xlink:to="loc_ifrs-full_Borrowings_c3185b92-2916-47a4-97fc-8b69c439a376" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CurrentAdvancesToSuppliers_f71fa34d-86f0-410b-b587-955b8b15c706" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CurrentAdvancesToSuppliers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOtherReceivablesAndOtherAssetsLineItems_a10b0bc7-6763-48f3-b274-5caeb6dabfef" xlink:to="loc_ifrs-full_CurrentAdvancesToSuppliers_f71fa34d-86f0-410b-b587-955b8b15c706" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ReclassificationOfPrepaidExpensesToCarryingValueOfDebtComponent_988a8a53-840e-427b-96c7-78ea09eeef8c" xlink:href="abvx-20251231.xsd#abvx_ReclassificationOfPrepaidExpensesToCarryingValueOfDebtComponent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOtherReceivablesAndOtherAssetsLineItems_a10b0bc7-6763-48f3-b274-5caeb6dabfef" xlink:to="loc_abvx_ReclassificationOfPrepaidExpensesToCarryingValueOfDebtComponent_988a8a53-840e-427b-96c7-78ea09eeef8c" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/CashandcashequivalentsNarrativeDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#CashandcashequivalentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/CashandcashequivalentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfCashAndCashEquivalentsLineItems_1fb3d627-69b2-443f-8dc7-bb23dc886c7b" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfCashAndCashEquivalentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfCashAndCashEquivalentsTable_92e45cfb-5e34-45be-95fc-2d4fcd9f0eb0" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfCashAndCashEquivalentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_abvx_DisclosureOfCashAndCashEquivalentsLineItems_1fb3d627-69b2-443f-8dc7-bb23dc886c7b" xlink:to="loc_abvx_DisclosureOfCashAndCashEquivalentsTable_92e45cfb-5e34-45be-95fc-2d4fcd9f0eb0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CurrencyAxis_b8d1da64-528f-44f0-8f8c-8bc25677364c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CurrencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfCashAndCashEquivalentsTable_92e45cfb-5e34-45be-95fc-2d4fcd9f0eb0" xlink:to="loc_srt_CurrencyAxis_b8d1da64-528f-44f0-8f8c-8bc25677364c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_b8d1da64-528f-44f0-8f8c-8bc25677364c_default" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CurrencyAxis_b8d1da64-528f-44f0-8f8c-8bc25677364c" xlink:to="loc_currency_AllCurrenciesDomain_b8d1da64-528f-44f0-8f8c-8bc25677364c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_84b6cee6-f74b-4a90-a7a4-1f7fda518047" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CurrencyAxis_b8d1da64-528f-44f0-8f8c-8bc25677364c" xlink:to="loc_currency_AllCurrenciesDomain_84b6cee6-f74b-4a90-a7a4-1f7fda518047" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_USD_ba51e457-528f-4306-8510-a7cd5767b17b" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_USD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_84b6cee6-f74b-4a90-a7a4-1f7fda518047" xlink:to="loc_currency_USD_ba51e457-528f-4306-8510-a7cd5767b17b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OtherCashAndCashEquivalents_45877975-8261-4cf9-9c7f-fc43dc3e9626" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherCashAndCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfCashAndCashEquivalentsLineItems_1fb3d627-69b2-443f-8dc7-bb23dc886c7b" xlink:to="loc_ifrs-full_OtherCashAndCashEquivalents_45877975-8261-4cf9-9c7f-fc43dc3e9626" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_EffectOfExchangeRateChangesOnCashAndCashEquivalents_56a6888a-64a7-4df9-966d-588a97d18f23" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_EffectOfExchangeRateChangesOnCashAndCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfCashAndCashEquivalentsLineItems_1fb3d627-69b2-443f-8dc7-bb23dc886c7b" xlink:to="loc_ifrs-full_EffectOfExchangeRateChangesOnCashAndCashEquivalents_56a6888a-64a7-4df9-966d-588a97d18f23" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialassetsandliabilitiesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialassetsandliabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialassetsandliabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesLineItems_09e7ea9e-0422-4834-b492-4b2471c70545" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesTable_eb61362b-324b-4ae6-93ae-5aeda5474a21" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesLineItems_09e7ea9e-0422-4834-b492-4b2471c70545" xlink:to="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesTable_eb61362b-324b-4ae6-93ae-5aeda5474a21" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfAssetsAxis_f49f844c-df61-4c3b-91f8-f4d99b28aa96" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfAssetsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesTable_eb61362b-324b-4ae6-93ae-5aeda5474a21" xlink:to="loc_ifrs-full_ClassesOfAssetsAxis_f49f844c-df61-4c3b-91f8-f4d99b28aa96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfAssetsDomain_f49f844c-df61-4c3b-91f8-f4d99b28aa96_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfAssetsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfAssetsAxis_f49f844c-df61-4c3b-91f8-f4d99b28aa96" xlink:to="loc_ifrs-full_ClassesOfAssetsDomain_f49f844c-df61-4c3b-91f8-f4d99b28aa96_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfAssetsDomain_4a466881-bf6b-4ef5-9313-b424dee5d840" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfAssetsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfAssetsAxis_f49f844c-df61-4c3b-91f8-f4d99b28aa96" xlink:to="loc_ifrs-full_ClassesOfAssetsDomain_4a466881-bf6b-4ef5-9313-b424dee5d840" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherFinancialAssetsMember_52644017-b6c3-4db6-a7d6-aa6c382b333e" xlink:href="abvx-20251231.xsd#abvx_OtherFinancialAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfAssetsDomain_4a466881-bf6b-4ef5-9313-b424dee5d840" xlink:to="loc_abvx_OtherFinancialAssetsMember_52644017-b6c3-4db6-a7d6-aa6c382b333e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherReceivablesAndAssetsMember_65c16dce-0677-4055-8a5d-d31f636ea10d" xlink:href="abvx-20251231.xsd#abvx_OtherReceivablesAndAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfAssetsDomain_4a466881-bf6b-4ef5-9313-b424dee5d840" xlink:to="loc_abvx_OtherReceivablesAndAssetsMember_65c16dce-0677-4055-8a5d-d31f636ea10d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CashAndCashEquivalentMember_dd1ef532-48ee-438b-9397-a6d8213b2dae" xlink:href="abvx-20251231.xsd#abvx_CashAndCashEquivalentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfAssetsDomain_4a466881-bf6b-4ef5-9313-b424dee5d840" xlink:to="loc_abvx_CashAndCashEquivalentMember_dd1ef532-48ee-438b-9397-a6d8213b2dae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NonCurrentAdvancesToCROContractsMember_1b75357c-dc00-4a9e-bd22-72a116a3053c" xlink:href="abvx-20251231.xsd#abvx_NonCurrentAdvancesToCROContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfAssetsDomain_4a466881-bf6b-4ef5-9313-b424dee5d840" xlink:to="loc_abvx_NonCurrentAdvancesToCROContractsMember_1b75357c-dc00-4a9e-bd22-72a116a3053c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_MeasurementAxis_2ac3fedd-b0a3-4ce8-bb8e-fd5cb702e443" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MeasurementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesTable_eb61362b-324b-4ae6-93ae-5aeda5474a21" xlink:to="loc_ifrs-full_MeasurementAxis_2ac3fedd-b0a3-4ce8-bb8e-fd5cb702e443" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_MeasurementDomain_2ac3fedd-b0a3-4ce8-bb8e-fd5cb702e443_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_MeasurementAxis_2ac3fedd-b0a3-4ce8-bb8e-fd5cb702e443" xlink:to="loc_ifrs-full_MeasurementDomain_2ac3fedd-b0a3-4ce8-bb8e-fd5cb702e443_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_MeasurementDomain_1fe30cca-a5d5-42d8-a66d-1cbab2bdb2fc" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_MeasurementAxis_2ac3fedd-b0a3-4ce8-bb8e-fd5cb702e443" xlink:to="loc_ifrs-full_MeasurementDomain_1fe30cca-a5d5-42d8-a66d-1cbab2bdb2fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RecurringFairValueMeasurementMember_c5f4c64a-8663-4063-a37f-9cba071bd895" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RecurringFairValueMeasurementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_MeasurementDomain_1fe30cca-a5d5-42d8-a66d-1cbab2bdb2fc" xlink:to="loc_ifrs-full_RecurringFairValueMeasurementMember_c5f4c64a-8663-4063-a37f-9cba071bd895" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CategoriesOfFinancialAssetsAxis_320f166b-17c7-484f-8f79-c1ba0e0b747b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfFinancialAssetsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesTable_eb61362b-324b-4ae6-93ae-5aeda5474a21" xlink:to="loc_ifrs-full_CategoriesOfFinancialAssetsAxis_320f166b-17c7-484f-8f79-c1ba0e0b747b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CategoriesOfFinancialAssetsDomain_320f166b-17c7-484f-8f79-c1ba0e0b747b_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfFinancialAssetsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_CategoriesOfFinancialAssetsAxis_320f166b-17c7-484f-8f79-c1ba0e0b747b" xlink:to="loc_ifrs-full_CategoriesOfFinancialAssetsDomain_320f166b-17c7-484f-8f79-c1ba0e0b747b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CategoriesOfFinancialAssetsDomain_79352162-f667-41e6-9571-c040c8740d83" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfFinancialAssetsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_CategoriesOfFinancialAssetsAxis_320f166b-17c7-484f-8f79-c1ba0e0b747b" xlink:to="loc_ifrs-full_CategoriesOfFinancialAssetsDomain_79352162-f667-41e6-9571-c040c8740d83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_FinancialAssetsAtFairValueThroughProfitOrLossCategoryMember_1bf2b0af-8068-436c-97b4-ea8dddc5dfdb" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FinancialAssetsAtFairValueThroughProfitOrLossCategoryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_CategoriesOfFinancialAssetsDomain_79352162-f667-41e6-9571-c040c8740d83" xlink:to="loc_ifrs-full_FinancialAssetsAtFairValueThroughProfitOrLossCategoryMember_1bf2b0af-8068-436c-97b4-ea8dddc5dfdb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_FinancialAssetsAtAmortisedCostCategoryMember_ee1ad156-1c91-4578-a410-557d5de7de3d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FinancialAssetsAtAmortisedCostCategoryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_CategoriesOfFinancialAssetsDomain_79352162-f667-41e6-9571-c040c8740d83" xlink:to="loc_ifrs-full_FinancialAssetsAtAmortisedCostCategoryMember_ee1ad156-1c91-4578-a410-557d5de7de3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CategoriesOfFinancialLiabilitiesAxis_2e93b70b-a581-462d-b88a-b6655a93ef56" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesTable_eb61362b-324b-4ae6-93ae-5aeda5474a21" xlink:to="loc_ifrs-full_CategoriesOfFinancialLiabilitiesAxis_2e93b70b-a581-462d-b88a-b6655a93ef56" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CategoriesOfFinancialLiabilitiesDomain_2e93b70b-a581-462d-b88a-b6655a93ef56_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_CategoriesOfFinancialLiabilitiesAxis_2e93b70b-a581-462d-b88a-b6655a93ef56" xlink:to="loc_ifrs-full_CategoriesOfFinancialLiabilitiesDomain_2e93b70b-a581-462d-b88a-b6655a93ef56_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CategoriesOfFinancialLiabilitiesDomain_d609931c-8eb2-464a-8409-3ac7dbb4901b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_CategoriesOfFinancialLiabilitiesAxis_2e93b70b-a581-462d-b88a-b6655a93ef56" xlink:to="loc_ifrs-full_CategoriesOfFinancialLiabilitiesDomain_d609931c-8eb2-464a-8409-3ac7dbb4901b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_FinancialLiabilitiesAtFairValueThroughProfitOrLossCategoryMember_37433730-c52a-4f43-ae66-951373fd042c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FinancialLiabilitiesAtFairValueThroughProfitOrLossCategoryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_CategoriesOfFinancialLiabilitiesDomain_d609931c-8eb2-464a-8409-3ac7dbb4901b" xlink:to="loc_ifrs-full_FinancialLiabilitiesAtFairValueThroughProfitOrLossCategoryMember_37433730-c52a-4f43-ae66-951373fd042c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_FinancialLiabilitiesAtAmortisedCostCategoryMember_8466749d-8c8e-4db4-83ed-1571e66de446" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FinancialLiabilitiesAtAmortisedCostCategoryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_CategoriesOfFinancialLiabilitiesDomain_d609931c-8eb2-464a-8409-3ac7dbb4901b" xlink:to="loc_ifrs-full_FinancialLiabilitiesAtAmortisedCostCategoryMember_8466749d-8c8e-4db4-83ed-1571e66de446" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfLiabilitiesAxis_f7327d89-bb6e-4b22-b236-a79f498c395e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesTable_eb61362b-324b-4ae6-93ae-5aeda5474a21" xlink:to="loc_ifrs-full_ClassesOfLiabilitiesAxis_f7327d89-bb6e-4b22-b236-a79f498c395e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfLiabilitiesDomain_f7327d89-bb6e-4b22-b236-a79f498c395e_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesAxis_f7327d89-bb6e-4b22-b236-a79f498c395e" xlink:to="loc_ifrs-full_ClassesOfLiabilitiesDomain_f7327d89-bb6e-4b22-b236-a79f498c395e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfLiabilitiesDomain_26b8a9a8-439f-4fd7-87c6-3b65978a4891" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesAxis_f7327d89-bb6e-4b22-b236-a79f498c395e" xlink:to="loc_ifrs-full_ClassesOfLiabilitiesDomain_26b8a9a8-439f-4fd7-87c6-3b65978a4891" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NonCurrentFinancialLiabilitiesMember_344a8d31-5afc-4e57-a9a2-ba69aede40cf" xlink:href="abvx-20251231.xsd#abvx_NonCurrentFinancialLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesDomain_26b8a9a8-439f-4fd7-87c6-3b65978a4891" xlink:to="loc_abvx_NonCurrentFinancialLiabilitiesMember_344a8d31-5afc-4e57-a9a2-ba69aede40cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheABAndCMember_ec1e8066-b74c-4e6f-b197-dea2ab89057e" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheABAndCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_NonCurrentFinancialLiabilitiesMember_344a8d31-5afc-4e57-a9a2-ba69aede40cf" xlink:to="loc_abvx_KreosClaretFinancingTrancheABAndCMember_ec1e8066-b74c-4e6f-b197-dea2ab89057e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheAMember_88dff9eb-fc96-4731-812e-97d206956a4d" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_NonCurrentFinancialLiabilitiesMember_344a8d31-5afc-4e57-a9a2-ba69aede40cf" xlink:to="loc_abvx_KreosClaretFinancingTrancheAMember_88dff9eb-fc96-4731-812e-97d206956a4d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConditionalAdvancesAndPGELoanMember_2adc2b84-a6ff-4a79-b9f6-fda6896c8838" xlink:href="abvx-20251231.xsd#abvx_ConditionalAdvancesAndPGELoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_NonCurrentFinancialLiabilitiesMember_344a8d31-5afc-4e57-a9a2-ba69aede40cf" xlink:to="loc_abvx_ConditionalAdvancesAndPGELoanMember_2adc2b84-a6ff-4a79-b9f6-fda6896c8838" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PretGarantiParLEtatPGEMember_73f63775-754b-4651-853d-c1e485841b98" xlink:href="abvx-20251231.xsd#abvx_PretGarantiParLEtatPGEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ConditionalAdvancesAndPGELoanMember_2adc2b84-a6ff-4a79-b9f6-fda6896c8838" xlink:to="loc_abvx_PretGarantiParLEtatPGEMember_73f63775-754b-4651-853d-c1e485841b98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RNPVIRConditionalAdvanceBPIMember_bcd5a293-0052-43e9-9d69-e0a4b801c4f4" xlink:href="abvx-20251231.xsd#abvx_RNPVIRConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ConditionalAdvancesAndPGELoanMember_2adc2b84-a6ff-4a79-b9f6-fda6896c8838" xlink:to="loc_abvx_RNPVIRConditionalAdvanceBPIMember_bcd5a293-0052-43e9-9d69-e0a4b801c4f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CARENAConditionalAdvanceBPIMember_011df764-fb31-4911-8002-8a796bf51aeb" xlink:href="abvx-20251231.xsd#abvx_CARENAConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ConditionalAdvancesAndPGELoanMember_2adc2b84-a6ff-4a79-b9f6-fda6896c8838" xlink:to="loc_abvx_CARENAConditionalAdvanceBPIMember_011df764-fb31-4911-8002-8a796bf51aeb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EbolaConditionalAdvanceBPIMember_6d73250c-5742-45ec-ae45-35540b8ecbd0" xlink:href="abvx-20251231.xsd#abvx_EbolaConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ConditionalAdvancesAndPGELoanMember_2adc2b84-a6ff-4a79-b9f6-fda6896c8838" xlink:to="loc_abvx_EbolaConditionalAdvanceBPIMember_6d73250c-5742-45ec-ae45-35540b8ecbd0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CurrentFinancialLiabilitiesMember_734b574c-24b1-4813-b05e-c07f763900ab" xlink:href="abvx-20251231.xsd#abvx_CurrentFinancialLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesDomain_26b8a9a8-439f-4fd7-87c6-3b65978a4891" xlink:to="loc_abvx_CurrentFinancialLiabilitiesMember_734b574c-24b1-4813-b05e-c07f763900ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TradePayablesAndOtherCurrentLiabilitiesMember_c77d82f8-2e89-4b62-a28a-8ce9b66c6e47" xlink:href="abvx-20251231.xsd#abvx_TradePayablesAndOtherCurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesDomain_26b8a9a8-439f-4fd7-87c6-3b65978a4891" xlink:to="loc_abvx_TradePayablesAndOtherCurrentLiabilitiesMember_c77d82f8-2e89-4b62-a28a-8ce9b66c6e47" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeAxis_44534e52-e837-4f59-b4c8-ecb6ffa66694" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesTable_eb61362b-324b-4ae6-93ae-5aeda5474a21" xlink:to="loc_ifrs-full_RangeAxis_44534e52-e837-4f59-b4c8-ecb6ffa66694" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_44534e52-e837-4f59-b4c8-ecb6ffa66694_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_RangeAxis_44534e52-e837-4f59-b4c8-ecb6ffa66694" xlink:to="loc_ifrs-full_RangeDomain_44534e52-e837-4f59-b4c8-ecb6ffa66694_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_55f71d54-bb2f-42fb-ad11-eb6bc4ac3eee" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_RangeAxis_44534e52-e837-4f59-b4c8-ecb6ffa66694" xlink:to="loc_ifrs-full_RangeDomain_55f71d54-bb2f-42fb-ad11-eb6bc4ac3eee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BottomOfRangeMember_df361df7-8a85-430a-87ff-6726fc49d742" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BottomOfRangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_55f71d54-bb2f-42fb-ad11-eb6bc4ac3eee" xlink:to="loc_ifrs-full_BottomOfRangeMember_df361df7-8a85-430a-87ff-6726fc49d742" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TopOfRangeMember_dd6fc551-5ef8-4e2d-b85d-cb93db53f34c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TopOfRangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_55f71d54-bb2f-42fb-ad11-eb6bc4ac3eee" xlink:to="loc_ifrs-full_TopOfRangeMember_dd6fc551-5ef8-4e2d-b85d-cb93db53f34c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsAxis_59168bdf-9890-47b7-8ea8-a51a8742e2df" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesTable_eb61362b-324b-4ae6-93ae-5aeda5474a21" xlink:to="loc_ifrs-full_UnobservableInputsAxis_59168bdf-9890-47b7-8ea8-a51a8742e2df" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_59168bdf-9890-47b7-8ea8-a51a8742e2df_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_UnobservableInputsAxis_59168bdf-9890-47b7-8ea8-a51a8742e2df" xlink:to="loc_ifrs-full_UnobservableInputsDomain_59168bdf-9890-47b7-8ea8-a51a8742e2df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_3396ecb8-4f80-4b36-a18e-773a7959d8b1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_UnobservableInputsAxis_59168bdf-9890-47b7-8ea8-a51a8742e2df" xlink:to="loc_ifrs-full_UnobservableInputsDomain_3396ecb8-4f80-4b36-a18e-773a7959d8b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CreditSpreadMeasurementInputMember_e62bd654-e27b-4784-9d0a-5626f3152f9f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CreditSpreadMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_3396ecb8-4f80-4b36-a18e-773a7959d8b1" xlink:to="loc_ifrs-full_CreditSpreadMeasurementInputMember_e62bd654-e27b-4784-9d0a-5626f3152f9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_96a573e2-ce6a-4ace-b3ef-c8670f34f270" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesTable_eb61362b-324b-4ae6-93ae-5aeda5474a21" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_96a573e2-ce6a-4ace-b3ef-c8670f34f270" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_96a573e2-ce6a-4ace-b3ef-c8670f34f270_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_96a573e2-ce6a-4ace-b3ef-c8670f34f270" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_96a573e2-ce6a-4ace-b3ef-c8670f34f270_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_f616dca6-9df4-48f5-884c-647b1a2e7bcc" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_96a573e2-ce6a-4ace-b3ef-c8670f34f270" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_f616dca6-9df4-48f5-884c-647b1a2e7bcc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DiscountedCashFlowMember_bd0b2db0-e34a-4e62-abf5-e9804a98ae6f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DiscountedCashFlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_f616dca6-9df4-48f5-884c-647b1a2e7bcc" xlink:to="loc_ifrs-full_DiscountedCashFlowMember_bd0b2db0-e34a-4e62-abf5-e9804a98ae6f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_Assets_d92189f6-06fa-4059-9d21-1642d0854fbf" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesLineItems_09e7ea9e-0422-4834-b492-4b2471c70545" xlink:to="loc_ifrs-full_Assets_d92189f6-06fa-4059-9d21-1642d0854fbf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_FinancialAssetsAtFairValue_fd86ecdf-126d-411f-af99-ab599cfc0514" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FinancialAssetsAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesLineItems_09e7ea9e-0422-4834-b492-4b2471c70545" xlink:to="loc_ifrs-full_FinancialAssetsAtFairValue_fd86ecdf-126d-411f-af99-ab599cfc0514" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_Liabilities_aefe6fe9-db2f-4404-b92d-50bb09210d9f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesLineItems_09e7ea9e-0422-4834-b492-4b2471c70545" xlink:to="loc_ifrs-full_Liabilities_aefe6fe9-db2f-4404-b92d-50bb09210d9f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_FinancialLiabilitiesAtFairValue_ccaf4fdb-9836-4fac-a9d2-d7f1dedebb0a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FinancialLiabilitiesAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesLineItems_09e7ea9e-0422-4834-b492-4b2471c70545" xlink:to="loc_ifrs-full_FinancialLiabilitiesAtFairValue_ccaf4fdb-9836-4fac-a9d2-d7f1dedebb0a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_SignificantUnobservableInputAssets_0976d20f-af14-4716-8fdc-d15bcf5bed09" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SignificantUnobservableInputAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesLineItems_09e7ea9e-0422-4834-b492-4b2471c70545" xlink:to="loc_ifrs-full_SignificantUnobservableInputAssets_0976d20f-af14-4716-8fdc-d15bcf5bed09" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputAssets_daf67fd2-92b3-4adf-b4cf-6382bd9383e6" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesLineItems_09e7ea9e-0422-4834-b492-4b2471c70545" xlink:to="loc_ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputAssets_daf67fd2-92b3-4adf-b4cf-6382bd9383e6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputAssets_46c7c057-2d32-4e53-b096-a5179dbc1b07" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesLineItems_09e7ea9e-0422-4834-b492-4b2471c70545" xlink:to="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputAssets_46c7c057-2d32-4e53-b096-a5179dbc1b07" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_SignificantUnobservableInputLiabilities_87435302-63e7-48d0-8713-d6c3c9e7e5f5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SignificantUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesLineItems_09e7ea9e-0422-4834-b492-4b2471c70545" xlink:to="loc_ifrs-full_SignificantUnobservableInputLiabilities_87435302-63e7-48d0-8713-d6c3c9e7e5f5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfTranches_019cfb72-9017-7599-b97d-e6ba1101d67d" xlink:href="abvx-20251231.xsd#abvx_NumberOfTranches"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesLineItems_09e7ea9e-0422-4834-b492-4b2471c70545" xlink:to="loc_abvx_NumberOfTranches_019cfb72-9017-7599-b97d-e6ba1101d67d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_ef643c7b-a0de-44ff-a148-05cacc40c4f9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesLineItems_09e7ea9e-0422-4834-b492-4b2471c70545" xlink:to="loc_ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_ef643c7b-a0de-44ff-a148-05cacc40c4f9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputLiabilities_a201f1e3-45b9-4da1-bc07-c2feff04be1d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFairValueMeasurementOfAssetsAndLiabilitiesLineItems_09e7ea9e-0422-4834-b492-4b2471c70545" xlink:to="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputLiabilities_a201f1e3-45b9-4da1-bc07-c2feff04be1d" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/ShareholdersequityChangeinsharecapitalDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#ShareholdersequityChangeinsharecapitalDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/ShareholdersequityChangeinsharecapitalDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfClassesOfShareCapitalLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfClassesOfShareCapitalTable_e58e1ca9-d480-4e76-8910-39b5321d45d0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfClassesOfShareCapitalTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_ifrs-full_DisclosureOfClassesOfShareCapitalTable_e58e1ca9-d480-4e76-8910-39b5321d45d0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialAgreementAxis_019bfa86-24aa-7a99-807a-d360dc28c9ca" xlink:href="abvx-20251231.xsd#abvx_FinancialAgreementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalTable_e58e1ca9-d480-4e76-8910-39b5321d45d0" xlink:to="loc_abvx_FinancialAgreementAxis_019bfa86-24aa-7a99-807a-d360dc28c9ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialAgreementDomain_019bfa86-24aa-7a99-807a-d360dc28c9ca_default" xlink:href="abvx-20251231.xsd#abvx_FinancialAgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_FinancialAgreementAxis_019bfa86-24aa-7a99-807a-d360dc28c9ca" xlink:to="loc_abvx_FinancialAgreementDomain_019bfa86-24aa-7a99-807a-d360dc28c9ca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialAgreementDomain_019bfa86-24aa-7309-b759-b7d0c6955d10" xlink:href="abvx-20251231.xsd#abvx_FinancialAgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_FinancialAgreementAxis_019bfa86-24aa-7a99-807a-d360dc28c9ca" xlink:to="loc_abvx_FinancialAgreementDomain_019bfa86-24aa-7309-b759-b7d0c6955d10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos1Member_019bfa86-24aa-74f0-8ac6-a8ccf4ff066e" xlink:href="abvx-20251231.xsd#abvx_Kreos1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FinancialAgreementDomain_019bfa86-24aa-7309-b759-b7d0c6955d10" xlink:to="loc_abvx_Kreos1Member_019bfa86-24aa-74f0-8ac6-a8ccf4ff066e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherEquityAgreementsMember_019bfa86-24aa-7b4a-9311-fbbaa02d1da0" xlink:href="abvx-20251231.xsd#abvx_OtherEquityAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FinancialAgreementDomain_019bfa86-24aa-7309-b759-b7d0c6955d10" xlink:to="loc_abvx_OtherEquityAgreementsMember_019bfa86-24aa-7b4a-9311-fbbaa02d1da0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019bfa86-24aa-74f7-9e66-58e0ed68f5dd" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalTable_e58e1ca9-d480-4e76-8910-39b5321d45d0" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019bfa86-24aa-74f7-9e66-58e0ed68f5dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019bfa86-24aa-74f7-9e66-58e0ed68f5dd_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019bfa86-24aa-74f7-9e66-58e0ed68f5dd" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019bfa86-24aa-74f7-9e66-58e0ed68f5dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019bfa86-24aa-7417-b9e8-6ad522db4ee4" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019bfa86-24aa-74f7-9e66-58e0ed68f5dd" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019bfa86-24aa-7417-b9e8-6ad522db4ee4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosABSAMember_019bfa86-24aa-7a20-b8de-d2bd0510a5e7" xlink:href="abvx-20251231.xsd#abvx_KreosABSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019bfa86-24aa-7417-b9e8-6ad522db4ee4" xlink:to="loc_abvx_KreosABSAMember_019bfa86-24aa-7a20-b8de-d2bd0510a5e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosBBSAMember_019bfa86-24aa-78f8-bf4b-a2736bb05fae" xlink:href="abvx-20251231.xsd#abvx_KreosBBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019bfa86-24aa-7417-b9e8-6ad522db4ee4" xlink:to="loc_abvx_KreosBBSAMember_019bfa86-24aa-78f8-bf4b-a2736bb05fae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20241AndBSA20242Member_019bfa86-53a9-786a-8bf1-3598b5e96816" xlink:href="abvx-20251231.xsd#abvx_BSA20241AndBSA20242Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019bfa86-24aa-7417-b9e8-6ad522db4ee4" xlink:to="loc_abvx_BSA20241AndBSA20242Member_019bfa86-53a9-786a-8bf1-3598b5e96816" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalAxis_019bfa86-24aa-7b29-b9f9-0570086cc6c1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalTable_e58e1ca9-d480-4e76-8910-39b5321d45d0" xlink:to="loc_ifrs-full_ClassesOfShareCapitalAxis_019bfa86-24aa-7b29-b9f9-0570086cc6c1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalDomain_019bfa86-24aa-7b29-b9f9-0570086cc6c1_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfShareCapitalAxis_019bfa86-24aa-7b29-b9f9-0570086cc6c1" xlink:to="loc_ifrs-full_ClassesOfShareCapitalDomain_019bfa86-24aa-7b29-b9f9-0570086cc6c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalDomain_019bfa86-24aa-7612-9513-2ed08055a57d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfShareCapitalAxis_019bfa86-24aa-7b29-b9f9-0570086cc6c1" xlink:to="loc_ifrs-full_ClassesOfShareCapitalDomain_019bfa86-24aa-7612-9513-2ed08055a57d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AmericanDepositorySharesMember_019bfa86-24aa-717d-8d8f-fc352e81dfd0" xlink:href="abvx-20251231.xsd#abvx_AmericanDepositorySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfShareCapitalDomain_019bfa86-24aa-7612-9513-2ed08055a57d" xlink:to="loc_abvx_AmericanDepositorySharesMember_019bfa86-24aa-717d-8d8f-fc352e81dfd0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OrdinarySharesMember_019bfa86-24aa-7f1b-8424-ba3339af547a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfShareCapitalDomain_019bfa86-24aa-7612-9513-2ed08055a57d" xlink:to="loc_ifrs-full_OrdinarySharesMember_019bfa86-24aa-7f1b-8424-ba3339af547a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_019bfa87-4537-7631-8dcb-be1b4b0b138f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalTable_e58e1ca9-d480-4e76-8910-39b5321d45d0" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_019bfa87-4537-7631-8dcb-be1b4b0b138f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019bfa87-4537-7631-8dcb-be1b4b0b138f_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019bfa87-4537-7631-8dcb-be1b4b0b138f" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019bfa87-4537-7631-8dcb-be1b4b0b138f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019bfa87-4537-7834-afdb-3de0a17312a3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019bfa87-4537-7631-8dcb-be1b4b0b138f" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019bfa87-4537-7834-afdb-3de0a17312a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_HeightsConvertibleNotesMember_019bfa87-4537-7fd9-beab-622facff8b44" xlink:href="abvx-20251231.xsd#abvx_HeightsConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bfa87-4537-7834-afdb-3de0a17312a3" xlink:to="loc_abvx_HeightsConvertibleNotesMember_019bfa87-4537-7fd9-beab-622facff8b44" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheAMember_019bfa87-4537-7bd7-b6c0-39825bc503b2" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bfa87-4537-7834-afdb-3de0a17312a3" xlink:to="loc_abvx_KreosClaretFinancingTrancheAMember_019bfa87-4537-7bd7-b6c0-39825bc503b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosABCBSAMember_019bfa88-8029-721f-a4ac-420aa8082b1d" xlink:href="abvx-20251231.xsd#abvx_KreosABCBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bfa87-4537-7834-afdb-3de0a17312a3" xlink:to="loc_abvx_KreosABCBSAMember_019bfa88-8029-721f-a4ac-420aa8082b1d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IssueOfEquity_019bfa86-24aa-7170-99d9-a6614e5871b8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IssueOfEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_ifrs-full_IssueOfEquity_019bfa86-24aa-7170-99d9-a6614e5871b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease_019bfa86-24aa-70b1-ad69-bb12227cab73" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease_019bfa86-24aa-70b1-ad69-bb12227cab73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ParValuePerShare_019bfa86-24aa-71cc-9cf7-cbf492ca3ef2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ParValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_ifrs-full_ParValuePerShare_019bfa86-24aa-71cc-9cf7-cbf492ca3ef2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EquityIssuanceSubscriptionPricePerShare_019bfa86-24aa-7916-b09b-f5d54b23010e" xlink:href="abvx-20251231.xsd#abvx_EquityIssuanceSubscriptionPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_abvx_EquityIssuanceSubscriptionPricePerShare_019bfa86-24aa-7916-b09b-f5d54b23010e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfWarrantsExercised_019bfa86-24aa-727c-88ac-df13439d1caf" xlink:href="abvx-20251231.xsd#abvx_NumberOfWarrantsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_abvx_NumberOfWarrantsExercised_019bfa86-24aa-727c-88ac-df13439d1caf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughExerciseOfWarrantsEquity_019bfa86-24aa-7762-8795-b4b2baa39cd9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughExerciseOfWarrantsEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughExerciseOfWarrantsEquity_019bfa86-24aa-7762-8795-b4b2baa39cd9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants_019bfa86-24aa-7868-b504-a1ad9d323300" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants_019bfa86-24aa-7868-b504-a1ad9d323300" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherShareWarrantsSubscriptionPricePerShare_019bfa86-24aa-70ca-95e2-de80b709d09b" xlink:href="abvx-20251231.xsd#abvx_OtherShareWarrantsSubscriptionPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_abvx_OtherShareWarrantsSubscriptionPricePerShare_019bfa86-24aa-70ca-95e2-de80b709d09b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IssueOfEquityOfferingPricePerShare_019bfa86-24aa-7a22-87c1-f4a838ccf2ef" xlink:href="abvx-20251231.xsd#abvx_IssueOfEquityOfferingPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_abvx_IssueOfEquityOfferingPricePerShare_019bfa86-24aa-7a22-87c1-f4a838ccf2ef" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ShareIssueRelatedCost_019bfa86-53a9-758c-86a4-ecedaf1b42fd" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ShareIssueRelatedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_ifrs-full_ShareIssueRelatedCost_019bfa86-53a9-758c-86a4-ecedaf1b42fd" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_019bfa86-53a9-7b13-8f4a-90235824e616" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_019bfa86-53a9-7b13-8f4a-90235824e616" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ShareWarrantsSubscriptionPricePerShare_019bfa86-53a9-713c-aa78-cf030ab56c03" xlink:href="abvx-20251231.xsd#abvx_ShareWarrantsSubscriptionPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_abvx_ShareWarrantsSubscriptionPricePerShare_019bfa86-53a9-713c-aa78-cf030ab56c03" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ShareIssueRelatedCostCredit_019bfa86-53a9-7237-af8e-4cc5d7abffc6" xlink:href="abvx-20251231.xsd#abvx_ShareIssueRelatedCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_abvx_ShareIssueRelatedCostCredit_019bfa86-53a9-7237-af8e-4cc5d7abffc6" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfFreeSharesIssued_019bfa86-53a9-77d3-bbbc-41053cd91fee" xlink:href="abvx-20251231.xsd#abvx_NumberOfFreeSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_abvx_NumberOfFreeSharesIssued_019bfa86-53a9-77d3-bbbc-41053cd91fee" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClosingForeignExchangeRate_019bfa87-4537-77c5-a40d-1c6bb036aeee" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClosingForeignExchangeRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_ifrs-full_ClosingForeignExchangeRate_019bfa87-4537-77c5-a40d-1c6bb036aeee" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfConvertibleNotesConverted_019bfa87-4537-705d-815a-8d80be363531" xlink:href="abvx-20251231.xsd#abvx_NumberOfConvertibleNotesConverted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_abvx_NumberOfConvertibleNotesConverted_019bfa87-4537-705d-815a-8d80be363531" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NotionalAmount_019bfa87-4537-7384-ac02-81da5da547d7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_ifrs-full_NotionalAmount_019bfa87-4537-7384-ac02-81da5da547d7" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseInNumberOfOrdinarySharesIssued_019bfa87-4537-7436-aca3-e0c8fa71edad" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseInNumberOfOrdinarySharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_ifrs-full_IncreaseDecreaseInNumberOfOrdinarySharesIssued_019bfa87-4537-7436-aca3-e0c8fa71edad" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsFixedConversionPrice_019bfa87-4537-7e91-823a-f534e01b47d0" xlink:href="abvx-20251231.xsd#abvx_BorrowingsFixedConversionPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_019bfa86-24aa-7469-b7d9-5c60420ce7f8" xlink:to="loc_abvx_BorrowingsFixedConversionPrice_019bfa87-4537-7e91-823a-f534e01b47d0" xlink:type="arc" order="18"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/SharebasedpaymentsDisclosureofreconciliationofBCEsDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#SharebasedpaymentsDisclosureofreconciliationofBCEsDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/SharebasedpaymentsDisclosureofreconciliationofBCEsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_1d70bcfd-e943-4d77-aa94-f5740d0584dc" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_47dea508-c7ee-486d-a2c3-c3ddd34011a9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_1d70bcfd-e943-4d77-aa94-f5740d0584dc" xlink:to="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_47dea508-c7ee-486d-a2c3-c3ddd34011a9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_6f35c44f-488b-436d-9391-01650ef7dbdd" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_47dea508-c7ee-486d-a2c3-c3ddd34011a9" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_6f35c44f-488b-436d-9391-01650ef7dbdd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_6f35c44f-488b-436d-9391-01650ef7dbdd_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_6f35c44f-488b-436d-9391-01650ef7dbdd" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_6f35c44f-488b-436d-9391-01650ef7dbdd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_2ac46ceb-b144-458e-a0b0-e10964858a9b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_6f35c44f-488b-436d-9391-01650ef7dbdd" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_2ac46ceb-b144-458e-a0b0-e10964858a9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_61ca9cc3-1332-45a6-b1dc-f0c7b0d89e26" xlink:href="abvx-20251231.xsd#abvx_FoundersShareSubscriptionWarrantsBCEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_2ac46ceb-b144-458e-a0b0-e10964858a9b" xlink:to="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_61ca9cc3-1332-45a6-b1dc-f0c7b0d89e26" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BCE20161Member_498a3203-7d46-4df9-baf6-6f5a77cfa1c9" xlink:href="abvx-20251231.xsd#abvx_BCE20161Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_61ca9cc3-1332-45a6-b1dc-f0c7b0d89e26" xlink:to="loc_abvx_BCE20161Member_498a3203-7d46-4df9-baf6-6f5a77cfa1c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BCE20171Member_4ecb7f9b-29c7-4cc3-9ae6-ced313e7775a" xlink:href="abvx-20251231.xsd#abvx_BCE20171Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_61ca9cc3-1332-45a6-b1dc-f0c7b0d89e26" xlink:to="loc_abvx_BCE20171Member_4ecb7f9b-29c7-4cc3-9ae6-ced313e7775a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BCE20172Member_36a5a6a5-a800-4e7f-bad4-95470f301f86" xlink:href="abvx-20251231.xsd#abvx_BCE20172Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_61ca9cc3-1332-45a6-b1dc-f0c7b0d89e26" xlink:to="loc_abvx_BCE20172Member_36a5a6a5-a800-4e7f-bad4-95470f301f86" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BCE20174Member_c46a2a79-5ba7-4e7b-9883-bc7efd32bb48" xlink:href="abvx-20251231.xsd#abvx_BCE20174Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_61ca9cc3-1332-45a6-b1dc-f0c7b0d89e26" xlink:to="loc_abvx_BCE20174Member_c46a2a79-5ba7-4e7b-9883-bc7efd32bb48" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BCE20175Member_55fead39-06f1-4186-a01a-51742757defd" xlink:href="abvx-20251231.xsd#abvx_BCE20175Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_61ca9cc3-1332-45a6-b1dc-f0c7b0d89e26" xlink:to="loc_abvx_BCE20175Member_55fead39-06f1-4186-a01a-51742757defd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BCE20181Member_ce1065e6-7182-463c-9cbf-7930431cf5a4" xlink:href="abvx-20251231.xsd#abvx_BCE20181Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_61ca9cc3-1332-45a6-b1dc-f0c7b0d89e26" xlink:to="loc_abvx_BCE20181Member_ce1065e6-7182-463c-9cbf-7930431cf5a4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BCE20184Member_e9aa6b70-2b6c-4e15-b44d-f19389dc9c79" xlink:href="abvx-20251231.xsd#abvx_BCE20184Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_61ca9cc3-1332-45a6-b1dc-f0c7b0d89e26" xlink:to="loc_abvx_BCE20184Member_e9aa6b70-2b6c-4e15-b44d-f19389dc9c79" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BCE20185Member_1a57f2f6-d4fe-450a-b50b-20d1fe96ce00" xlink:href="abvx-20251231.xsd#abvx_BCE20185Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_61ca9cc3-1332-45a6-b1dc-f0c7b0d89e26" xlink:to="loc_abvx_BCE20185Member_1a57f2f6-d4fe-450a-b50b-20d1fe96ce00" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement_42b01723-aa96-4940-a89f-f1447502cac2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_1d70bcfd-e943-4d77-aa94-f5740d0584dc" xlink:to="loc_ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement_42b01723-aa96-4940-a89f-f1447502cac2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_290de5b4-eb4e-499c-90f3-438f7b0c5061" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_1d70bcfd-e943-4d77-aa94-f5740d0584dc" xlink:to="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_290de5b4-eb4e-499c-90f3-438f7b0c5061" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfOtherEquityInstrumentsExpiredInSharebasedPaymentArrangement_96d33b93-56d7-45e8-8a5b-413116a0a6a5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfOtherEquityInstrumentsExpiredInSharebasedPaymentArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_1d70bcfd-e943-4d77-aa94-f5740d0584dc" xlink:to="loc_ifrs-full_NumberOfOtherEquityInstrumentsExpiredInSharebasedPaymentArrangement_96d33b93-56d7-45e8-8a5b-413116a0a6a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfOtherEquityInstrumentsExercisedOrVestedInSharebasedPaymentArrangement_c6cb33c8-6cb5-4224-ad30-5447a6bb2c63" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfOtherEquityInstrumentsExercisedOrVestedInSharebasedPaymentArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_1d70bcfd-e943-4d77-aa94-f5740d0584dc" xlink:to="loc_ifrs-full_NumberOfOtherEquityInstrumentsExercisedOrVestedInSharebasedPaymentArrangement_c6cb33c8-6cb5-4224-ad30-5447a6bb2c63" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement_882fddcb-be7a-4f48-a5a3-1c4b62612f54" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfOtherEquityInstrumentsExercisableInSharebasedPaymentArrangement_9a200f7b-3c9d-4a9d-b84e-9a9c21216d4d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfOtherEquityInstrumentsExercisableInSharebasedPaymentArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_1d70bcfd-e943-4d77-aa94-f5740d0584dc" xlink:to="loc_ifrs-full_NumberOfOtherEquityInstrumentsExercisableInSharebasedPaymentArrangement_9a200f7b-3c9d-4a9d-b84e-9a9c21216d4d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_MaximumNumberOfOtherEquityInstrumentsToBeIssuedInShareBasedPaymentArrangementIfAllConditionsAreMet_96c6d517-0ab9-4ad8-b56e-f948a27c24e4" xlink:href="abvx-20251231.xsd#abvx_MaximumNumberOfOtherEquityInstrumentsToBeIssuedInShareBasedPaymentArrangementIfAllConditionsAreMet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_1d70bcfd-e943-4d77-aa94-f5740d0584dc" xlink:to="loc_abvx_MaximumNumberOfOtherEquityInstrumentsToBeIssuedInShareBasedPaymentArrangementIfAllConditionsAreMet_96c6d517-0ab9-4ad8-b56e-f948a27c24e4" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/SharebasedpaymentsNarrativeDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#SharebasedpaymentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/SharebasedpaymentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_019bfb19-cfb8-7bdc-b888-cd33594b4482" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_9a4168f3-5cd7-4898-92d5-32efd93d22ec" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_019bfb19-cfb8-7bdc-b888-cd33594b4482" xlink:to="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_9a4168f3-5cd7-4898-92d5-32efd93d22ec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesAxis_019bfb19-cfb8-7f14-8c83-e80db55db7bb" xlink:href="abvx-20251231.xsd#abvx_TranchesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_9a4168f3-5cd7-4898-92d5-32efd93d22ec" xlink:to="loc_abvx_TranchesAxis_019bfb19-cfb8-7f14-8c83-e80db55db7bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesDomain_019bfb19-cfb8-7f14-8c83-e80db55db7bb_default" xlink:href="abvx-20251231.xsd#abvx_TranchesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_TranchesAxis_019bfb19-cfb8-7f14-8c83-e80db55db7bb" xlink:to="loc_abvx_TranchesDomain_019bfb19-cfb8-7f14-8c83-e80db55db7bb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesDomain_019bfb19-cfb8-716f-bb26-edacd9711228" xlink:href="abvx-20251231.xsd#abvx_TranchesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_TranchesAxis_019bfb19-cfb8-7f14-8c83-e80db55db7bb" xlink:to="loc_abvx_TranchesDomain_019bfb19-cfb8-716f-bb26-edacd9711228" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheOneMember_019bfb19-cfb8-7ced-a345-7726767b6e22" xlink:href="abvx-20251231.xsd#abvx_TrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_019bfb19-cfb8-716f-bb26-edacd9711228" xlink:to="loc_abvx_TrancheOneMember_019bfb19-cfb8-7ced-a345-7726767b6e22" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheTwoMember_019bfb19-cfb8-7abf-983e-3bfbd749f314" xlink:href="abvx-20251231.xsd#abvx_TrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_019bfb19-cfb8-716f-bb26-edacd9711228" xlink:to="loc_abvx_TrancheTwoMember_019bfb19-cfb8-7abf-983e-3bfbd749f314" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheThreeMember_019bfb1a-6596-7278-a0f4-9e910b437217" xlink:href="abvx-20251231.xsd#abvx_TrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_019bfb19-cfb8-716f-bb26-edacd9711228" xlink:to="loc_abvx_TrancheThreeMember_019bfb1a-6596-7278-a0f4-9e910b437217" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheFourMember_019bfb1a-6596-7dc5-adde-72d66cca39d9" xlink:href="abvx-20251231.xsd#abvx_TrancheFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_019bfb19-cfb8-716f-bb26-edacd9711228" xlink:to="loc_abvx_TrancheFourMember_019bfb1a-6596-7dc5-adde-72d66cca39d9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheFiveMember_019bfb1a-6596-733e-ae7d-82d66176bd78" xlink:href="abvx-20251231.xsd#abvx_TrancheFiveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_019bfb19-cfb8-716f-bb26-edacd9711228" xlink:to="loc_abvx_TrancheFiveMember_019bfb1a-6596-733e-ae7d-82d66176bd78" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheSixMember_019bfb1a-6596-7047-8b7e-3e3e8a995f8c" xlink:href="abvx-20251231.xsd#abvx_TrancheSixMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_019bfb19-cfb8-716f-bb26-edacd9711228" xlink:to="loc_abvx_TrancheSixMember_019bfb1a-6596-7047-8b7e-3e3e8a995f8c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019bfb19-cfb8-7e04-92ff-fad51b249078" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_9a4168f3-5cd7-4898-92d5-32efd93d22ec" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019bfb19-cfb8-7e04-92ff-fad51b249078" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019bfb19-cfb8-7e04-92ff-fad51b249078_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019bfb19-cfb8-7e04-92ff-fad51b249078" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019bfb19-cfb8-7e04-92ff-fad51b249078_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019bfb19-cfb8-73e5-9124-e484181a565a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_019bfb19-cfb8-7e04-92ff-fad51b249078" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019bfb19-cfb8-73e5-9124-e484181a565a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_019bfb19-cfb8-7d69-9df0-e21350266eba" xlink:href="abvx-20251231.xsd#abvx_FoundersShareSubscriptionWarrantsBCEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019bfb19-cfb8-73e5-9124-e484181a565a" xlink:to="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_019bfb19-cfb8-7d69-9df0-e21350266eba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BCEExceptBCE20142Member_019bfb19-cfb8-7d99-8c0b-d850fa892a85" xlink:href="abvx-20251231.xsd#abvx_BCEExceptBCE20142Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_019bfb19-cfb8-7d69-9df0-e21350266eba" xlink:to="loc_abvx_BCEExceptBCE20142Member_019bfb19-cfb8-7d99-8c0b-d850fa892a85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ShareSubscriptionWarrantsBSAMember_019bfb19-ffde-700f-bf2a-d7e8e0543807" xlink:href="abvx-20251231.xsd#abvx_ShareSubscriptionWarrantsBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019bfb19-cfb8-73e5-9124-e484181a565a" xlink:to="loc_abvx_ShareSubscriptionWarrantsBSAMember_019bfb19-ffde-700f-bf2a-d7e8e0543807" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20241AndBSA20242Member_019bfb19-ffde-73c4-bb5b-fdd052f7f560" xlink:href="abvx-20251231.xsd#abvx_BSA20241AndBSA20242Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ShareSubscriptionWarrantsBSAMember_019bfb19-ffde-700f-bf2a-d7e8e0543807" xlink:to="loc_abvx_BSA20241AndBSA20242Member_019bfb19-ffde-73c4-bb5b-fdd052f7f560" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20251AndBSA20252Member_019cfca6-e954-7cc4-af1a-50d187713e4f" xlink:href="abvx-20251231.xsd#abvx_BSA20251AndBSA20252Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ShareSubscriptionWarrantsBSAMember_019bfb19-ffde-700f-bf2a-d7e8e0543807" xlink:to="loc_abvx_BSA20251AndBSA20252Member_019cfca6-e954-7cc4-af1a-50d187713e4f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20253Member_019cfca7-11b1-7957-9736-d8d9439463d6" xlink:href="abvx-20251231.xsd#abvx_BSA20253Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ShareSubscriptionWarrantsBSAMember_019bfb19-ffde-700f-bf2a-d7e8e0543807" xlink:to="loc_abvx_BSA20253Member_019cfca7-11b1-7957-9736-d8d9439463d6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:href="abvx-20251231.xsd#abvx_FreeSharesAGAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_019bfb19-cfb8-73e5-9124-e484181a565a" xlink:to="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20231Member_019bfb1a-6596-7e1d-8857-dadfbad3540e" xlink:href="abvx-20251231.xsd#abvx_AGA20231Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20231Member_019bfb1a-6596-7e1d-8857-dadfbad3540e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20232Member_019bfb1a-9ecc-7c8d-abf9-8ec3a724dc19" xlink:href="abvx-20251231.xsd#abvx_AGA20232Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20232Member_019bfb1a-9ecc-7c8d-abf9-8ec3a724dc19" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20233AGA20234AndAGA20235Member_019bfb1a-9ecc-7273-b1dc-22738c7dd6c1" xlink:href="abvx-20251231.xsd#abvx_AGA20233AGA20234AndAGA20235Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20233AGA20234AndAGA20235Member_019bfb1a-9ecc-7273-b1dc-22738c7dd6c1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20233AndAGA20234Member_019bfb1a-9ecc-75b3-8e84-bd99ad3724b7" xlink:href="abvx-20251231.xsd#abvx_AGA20233AndAGA20234Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_AGA20233AGA20234AndAGA20235Member_019bfb1a-9ecc-7273-b1dc-22738c7dd6c1" xlink:to="loc_abvx_AGA20233AndAGA20234Member_019bfb1a-9ecc-75b3-8e84-bd99ad3724b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20235Member_019bfb1a-9ecc-7962-a059-e83010e81e35" xlink:href="abvx-20251231.xsd#abvx_AGA20235Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_AGA20233AGA20234AndAGA20235Member_019bfb1a-9ecc-7273-b1dc-22738c7dd6c1" xlink:to="loc_abvx_AGA20235Member_019bfb1a-9ecc-7962-a059-e83010e81e35" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20241Member_019bfb1a-c1ca-799b-808f-cf0ea4e9958d" xlink:href="abvx-20251231.xsd#abvx_AGA20241Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20241Member_019bfb1a-c1ca-799b-808f-cf0ea4e9958d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20242Member_019bfb1a-c1ca-70e5-8efa-6fedf1943926" xlink:href="abvx-20251231.xsd#abvx_AGA20242Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20242Member_019bfb1a-c1ca-70e5-8efa-6fedf1943926" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20243Member_019bfb1a-c1ca-7812-a457-ceff09f8665e" xlink:href="abvx-20251231.xsd#abvx_AGA20243Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20243Member_019bfb1a-c1ca-7812-a457-ceff09f8665e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20244AGA20245AndAGA20246Member_019bfb1a-c1ca-76fe-80a0-22b94d947eac" xlink:href="abvx-20251231.xsd#abvx_AGA20244AGA20245AndAGA20246Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20244AGA20245AndAGA20246Member_019bfb1a-c1ca-76fe-80a0-22b94d947eac" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20247Member_019bfb1a-c1ca-74f5-a5ec-9ca29f46bc53" xlink:href="abvx-20251231.xsd#abvx_AGA20247Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20247Member_019bfb1a-c1ca-74f5-a5ec-9ca29f46bc53" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20241AGE20242AGA20243AGA20244AGA20245AndAGA20247Member_019bfb1a-ecc0-7e9a-9bff-84d460153dfb" xlink:href="abvx-20251231.xsd#abvx_AGA20241AGE20242AGA20243AGA20244AGA20245AndAGA20247Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20241AGE20242AGA20243AGA20244AGA20245AndAGA20247Member_019bfb1a-ecc0-7e9a-9bff-84d460153dfb" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20246Member_019bfb1a-ecc0-7dd8-99df-83e27c86b936" xlink:href="abvx-20251231.xsd#abvx_AGA20246Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20246Member_019bfb1a-ecc0-7dd8-99df-83e27c86b936" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20251Member_019bfb1b-2608-7a81-9ce5-8a31a8f4f904" xlink:href="abvx-20251231.xsd#abvx_AGA20251Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20251Member_019bfb1b-2608-7a81-9ce5-8a31a8f4f904" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20252Member_019bfb1b-2608-73da-ad7e-294b5a7fd7b0" xlink:href="abvx-20251231.xsd#abvx_AGA20252Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20252Member_019bfb1b-2608-73da-ad7e-294b5a7fd7b0" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20253Member_019bfb1b-2608-792e-8965-7e86c4ab9f12" xlink:href="abvx-20251231.xsd#abvx_AGA20253Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20253Member_019bfb1b-2608-792e-8965-7e86c4ab9f12" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20254Member_019bfb1b-2608-7182-b0a6-dde36dbc0779" xlink:href="abvx-20251231.xsd#abvx_AGA20254Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20254Member_019bfb1b-2608-7182-b0a6-dde36dbc0779" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20256Member_019bfb1b-2608-7e24-89ca-ddc6be2ae4f3" xlink:href="abvx-20251231.xsd#abvx_AGA20256Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20256Member_019bfb1b-2608-7e24-89ca-ddc6be2ae4f3" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20257Member_019bfb1b-2608-72a0-8281-5d521eb13a98" xlink:href="abvx-20251231.xsd#abvx_AGA20257Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20257Member_019bfb1b-2608-72a0-8281-5d521eb13a98" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20258Member_019bfb1b-2608-7d70-9a0a-017c7b24c302" xlink:href="abvx-20251231.xsd#abvx_AGA20258Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20258Member_019bfb1b-2608-7d70-9a0a-017c7b24c302" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20251AGA20253AGA20254AGA20256AGA20257AndAGA20258Member_019bfb1b-2608-7462-8e98-f1d5ed173a96" xlink:href="abvx-20251231.xsd#abvx_AGA20251AGA20253AGA20254AGA20256AGA20257AndAGA20258Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20251AGA20253AGA20254AGA20256AGA20257AndAGA20258Member_019bfb1b-2608-7462-8e98-f1d5ed173a96" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20255Member_019bfb1b-2608-709f-af24-dbe111b5e67f" xlink:href="abvx-20251231.xsd#abvx_AGA20255Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_019cf672-bed8-7b05-85fa-789b45d227fc" xlink:to="loc_abvx_AGA20255Member_019bfb1b-2608-709f-af24-dbe111b5e67f" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_019bfb1a-35f5-7b16-80e0-18b961afac81" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_9a4168f3-5cd7-4898-92d5-32efd93d22ec" xlink:to="loc_srt_TitleOfIndividualAxis_019bfb1a-35f5-7b16-80e0-18b961afac81" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019bfb1a-35f5-7b16-80e0-18b961afac81_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_019bfb1a-35f5-7b16-80e0-18b961afac81" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019bfb1a-35f5-7b16-80e0-18b961afac81_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019bfb1a-35f5-7452-b953-1ca7edba1eee" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_019bfb1a-35f5-7b16-80e0-18b961afac81" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019bfb1a-35f5-7452-b953-1ca7edba1eee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ChiefExecutiveOfficerMember_019bfb1a-6596-70c3-bb9c-f9f9159d7884" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ChiefExecutiveOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019bfb1a-35f5-7452-b953-1ca7edba1eee" xlink:to="loc_srt_ChiefExecutiveOfficerMember_019bfb1a-6596-70c3-bb9c-f9f9159d7884" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FormerChiefExecutiveOfficerMember_019bfb1a-9ecc-7fc6-8c12-68166810e396" xlink:href="abvx-20251231.xsd#abvx_FormerChiefExecutiveOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019bfb1a-35f5-7452-b953-1ca7edba1eee" xlink:to="loc_abvx_FormerChiefExecutiveOfficerMember_019bfb1a-9ecc-7fc6-8c12-68166810e396" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EmployeeMember_019bfb1a-ecc0-7419-897c-a4485c752907" xlink:href="abvx-20251231.xsd#abvx_EmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019bfb1a-35f5-7452-b953-1ca7edba1eee" xlink:to="loc_abvx_EmployeeMember_019bfb1a-ecc0-7419-897c-a4485c752907" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019c003f-1ea0-7383-892d-3ee631562258" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_9a4168f3-5cd7-4898-92d5-32efd93d22ec" xlink:to="loc_srt_RangeAxis_019c003f-1ea0-7383-892d-3ee631562258" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c003f-1ea0-7383-892d-3ee631562258_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019c003f-1ea0-7383-892d-3ee631562258" xlink:to="loc_srt_RangeMember_019c003f-1ea0-7383-892d-3ee631562258_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c003f-1ea0-71ee-95e7-2364dce30b77" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019c003f-1ea0-7383-892d-3ee631562258" xlink:to="loc_srt_RangeMember_019c003f-1ea0-71ee-95e7-2364dce30b77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019c003f-1ea0-7315-bf2f-bdaea9a2a338" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c003f-1ea0-71ee-95e7-2364dce30b77" xlink:to="loc_srt_MaximumMember_019c003f-1ea0-7315-bf2f-bdaea9a2a338" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentage_019bfb19-cfb8-7d4c-82b8-d01782bc92a0" xlink:href="abvx-20251231.xsd#abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_019bfb19-cfb8-7bdc-b888-cd33594b4482" xlink:to="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentage_019bfb19-cfb8-7d4c-82b8-d01782bc92a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPeriod_019bfb19-cfb8-73bb-be84-74d1b2bd6dfd" xlink:href="abvx-20251231.xsd#abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_019bfb19-cfb8-7bdc-b888-cd33594b4482" xlink:to="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPeriod_019bfb19-cfb8-73bb-be84-74d1b2bd6dfd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentagePerMonth_019c003f-1ea0-741d-936d-2591217db816" xlink:href="abvx-20251231.xsd#abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentagePerMonth"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_019bfb19-cfb8-7bdc-b888-cd33594b4482" xlink:to="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementVestingPercentagePerMonth_019c003f-1ea0-741d-936d-2591217db816" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementPerformanceConditionsMinimumFinancing_019bfb19-cfb8-7200-84ea-ed39355e284e" xlink:href="abvx-20251231.xsd#abvx_VestingRequirementsForShareBasedPaymentArrangementPerformanceConditionsMinimumFinancing"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_019bfb19-cfb8-7bdc-b888-cd33594b4482" xlink:to="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementPerformanceConditionsMinimumFinancing_019bfb19-cfb8-7200-84ea-ed39355e284e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementChangeOfControlMinimumThreshold_019bfb19-cfb8-70cb-a7b9-e7cd4e80df92" xlink:href="abvx-20251231.xsd#abvx_VestingRequirementsForShareBasedPaymentArrangementChangeOfControlMinimumThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_019bfb19-cfb8-7bdc-b888-cd33594b4482" xlink:to="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementChangeOfControlMinimumThreshold_019bfb19-cfb8-70cb-a7b9-e7cd4e80df92" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_019bfb19-ffde-7065-af49-483278da772c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_019bfb19-cfb8-7bdc-b888-cd33594b4482" xlink:to="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_019bfb19-ffde-7065-af49-483278da772c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfOtherEquityInstrumentsGrantedSubjectToNonMarketPerformanceCondition_019bfb1a-9ecc-7cb6-b681-019e1960914e" xlink:href="abvx-20251231.xsd#abvx_NumberOfOtherEquityInstrumentsGrantedSubjectToNonMarketPerformanceCondition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_019bfb19-cfb8-7bdc-b888-cd33594b4482" xlink:to="loc_abvx_NumberOfOtherEquityInstrumentsGrantedSubjectToNonMarketPerformanceCondition_019bfb1a-9ecc-7cb6-b681-019e1960914e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OtherShorttermProvisions_019bfb1b-530a-7bae-8355-94f5d2dc56df" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherShorttermProvisions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_019bfb19-cfb8-7bdc-b888-cd33594b4482" xlink:to="loc_ifrs-full_OtherShorttermProvisions_019bfb1b-530a-7bae-8355-94f5d2dc56df" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OtherLongtermProvisions_019bfb1b-530a-741c-b825-572d1e3314ae" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherLongtermProvisions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_019bfb19-cfb8-7bdc-b888-cd33594b4482" xlink:to="loc_ifrs-full_OtherLongtermProvisions_019bfb1b-530a-741c-b825-572d1e3314ae" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementServicePeriod_019c003f-1ea0-7e35-affe-c5e8e9a7fbeb" xlink:href="abvx-20251231.xsd#abvx_VestingRequirementsForShareBasedPaymentArrangementServicePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_019bfb19-cfb8-7bdc-b888-cd33594b4482" xlink:to="loc_abvx_VestingRequirementsForShareBasedPaymentArrangementServicePeriod_019c003f-1ea0-7e35-affe-c5e8e9a7fbeb" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/SharebasedpaymentsDisclosureofreconciliationofBSAsDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#SharebasedpaymentsDisclosureofreconciliationofBSAsDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/SharebasedpaymentsDisclosureofreconciliationofBSAsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_8ed354f7-adab-4275-a35c-87a9f9aa4244" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_3fcb40b1-6499-4202-8d89-edcafd8fb34f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_8ed354f7-adab-4275-a35c-87a9f9aa4244" xlink:to="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_3fcb40b1-6499-4202-8d89-edcafd8fb34f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_f606e404-67e1-44c5-835a-311bee9e4692" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_3fcb40b1-6499-4202-8d89-edcafd8fb34f" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_f606e404-67e1-44c5-835a-311bee9e4692" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_f606e404-67e1-44c5-835a-311bee9e4692_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_f606e404-67e1-44c5-835a-311bee9e4692" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_f606e404-67e1-44c5-835a-311bee9e4692_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_d787b95a-8181-48bc-8679-eb961a9b5a7a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_f606e404-67e1-44c5-835a-311bee9e4692" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_d787b95a-8181-48bc-8679-eb961a9b5a7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ShareSubscriptionWarrantsBSAMember_86827a7c-0da6-4a99-8bf0-6ba3f8a0722b" xlink:href="abvx-20251231.xsd#abvx_ShareSubscriptionWarrantsBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_d787b95a-8181-48bc-8679-eb961a9b5a7a" xlink:to="loc_abvx_ShareSubscriptionWarrantsBSAMember_86827a7c-0da6-4a99-8bf0-6ba3f8a0722b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA201511Member_5145e119-555e-45b8-92d6-477edd40d794" xlink:href="abvx-20251231.xsd#abvx_BSA201511Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ShareSubscriptionWarrantsBSAMember_86827a7c-0da6-4a99-8bf0-6ba3f8a0722b" xlink:to="loc_abvx_BSA201511Member_5145e119-555e-45b8-92d6-477edd40d794" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA201512Member_953c6161-1140-4bde-94f9-1aa77579036e" xlink:href="abvx-20251231.xsd#abvx_BSA201512Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ShareSubscriptionWarrantsBSAMember_86827a7c-0da6-4a99-8bf0-6ba3f8a0722b" xlink:to="loc_abvx_BSA201512Member_953c6161-1140-4bde-94f9-1aa77579036e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20171Member_b871846b-d010-4b1d-871e-0bdeca850833" xlink:href="abvx-20251231.xsd#abvx_BSA20171Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ShareSubscriptionWarrantsBSAMember_86827a7c-0da6-4a99-8bf0-6ba3f8a0722b" xlink:to="loc_abvx_BSA20171Member_b871846b-d010-4b1d-871e-0bdeca850833" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20181Member_6421f5ba-ed88-4263-ad6f-56e7cd2df058" xlink:href="abvx-20251231.xsd#abvx_BSA20181Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ShareSubscriptionWarrantsBSAMember_86827a7c-0da6-4a99-8bf0-6ba3f8a0722b" xlink:to="loc_abvx_BSA20181Member_6421f5ba-ed88-4263-ad6f-56e7cd2df058" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20241Member_0f8c245f-6182-41ac-9bc7-8a516fea38f7" xlink:href="abvx-20251231.xsd#abvx_BSA20241Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ShareSubscriptionWarrantsBSAMember_86827a7c-0da6-4a99-8bf0-6ba3f8a0722b" xlink:to="loc_abvx_BSA20241Member_0f8c245f-6182-41ac-9bc7-8a516fea38f7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20242Member_8e31b790-0927-40b5-afcb-d40365f990e7" xlink:href="abvx-20251231.xsd#abvx_BSA20242Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ShareSubscriptionWarrantsBSAMember_86827a7c-0da6-4a99-8bf0-6ba3f8a0722b" xlink:to="loc_abvx_BSA20242Member_8e31b790-0927-40b5-afcb-d40365f990e7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20251Member_019c5687-aadc-7f29-aedf-6355a3bb6308" xlink:href="abvx-20251231.xsd#abvx_BSA20251Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ShareSubscriptionWarrantsBSAMember_86827a7c-0da6-4a99-8bf0-6ba3f8a0722b" xlink:to="loc_abvx_BSA20251Member_019c5687-aadc-7f29-aedf-6355a3bb6308" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20252Member_019c5687-d130-7872-8cc5-d48403a0d1d0" xlink:href="abvx-20251231.xsd#abvx_BSA20252Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ShareSubscriptionWarrantsBSAMember_86827a7c-0da6-4a99-8bf0-6ba3f8a0722b" xlink:to="loc_abvx_BSA20252Member_019c5687-d130-7872-8cc5-d48403a0d1d0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20253Member_019c5687-f206-79f2-bbfd-90327dcae5ad" xlink:href="abvx-20251231.xsd#abvx_BSA20253Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ShareSubscriptionWarrantsBSAMember_86827a7c-0da6-4a99-8bf0-6ba3f8a0722b" xlink:to="loc_abvx_BSA20253Member_019c5687-f206-79f2-bbfd-90327dcae5ad" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement_8707e9c3-9c03-47c9-8cf9-9843c0e68fb1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_8ed354f7-adab-4275-a35c-87a9f9aa4244" xlink:to="loc_ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement_8707e9c3-9c03-47c9-8cf9-9843c0e68fb1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_ff6367f1-7763-4e11-bbb2-96b824c79ff0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_8ed354f7-adab-4275-a35c-87a9f9aa4244" xlink:to="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_ff6367f1-7763-4e11-bbb2-96b824c79ff0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfOtherEquityInstrumentsExpiredInSharebasedPaymentArrangement_9aba2688-3a5d-441f-80b2-52607984ad21" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfOtherEquityInstrumentsExpiredInSharebasedPaymentArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_8ed354f7-adab-4275-a35c-87a9f9aa4244" xlink:to="loc_ifrs-full_NumberOfOtherEquityInstrumentsExpiredInSharebasedPaymentArrangement_9aba2688-3a5d-441f-80b2-52607984ad21" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfOtherEquityInstrumentsExercisedOrVestedInSharebasedPaymentArrangement_9b61b9e8-6862-4ca5-b205-2746782ac62a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfOtherEquityInstrumentsExercisedOrVestedInSharebasedPaymentArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_8ed354f7-adab-4275-a35c-87a9f9aa4244" xlink:to="loc_ifrs-full_NumberOfOtherEquityInstrumentsExercisedOrVestedInSharebasedPaymentArrangement_9b61b9e8-6862-4ca5-b205-2746782ac62a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement_aff8bb19-ef3f-4d66-a621-7c29870824c9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfOtherEquityInstrumentsExercisableInSharebasedPaymentArrangement_c39eb5ae-d3ac-4566-95c8-cf9012596de9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfOtherEquityInstrumentsExercisableInSharebasedPaymentArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_8ed354f7-adab-4275-a35c-87a9f9aa4244" xlink:to="loc_ifrs-full_NumberOfOtherEquityInstrumentsExercisableInSharebasedPaymentArrangement_c39eb5ae-d3ac-4566-95c8-cf9012596de9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_MaximumNumberOfOtherEquityInstrumentsToBeIssuedInShareBasedPaymentArrangementIfAllConditionsAreMet_f348720e-3dda-4406-893f-3fac7b466bfa" xlink:href="abvx-20251231.xsd#abvx_MaximumNumberOfOtherEquityInstrumentsToBeIssuedInShareBasedPaymentArrangementIfAllConditionsAreMet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_8ed354f7-adab-4275-a35c-87a9f9aa4244" xlink:to="loc_abvx_MaximumNumberOfOtherEquityInstrumentsToBeIssuedInShareBasedPaymentArrangementIfAllConditionsAreMet_f348720e-3dda-4406-893f-3fac7b466bfa" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/SharebasedpaymentsDisclosureofassumptionsusedforthemeasurementofBSAsDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#SharebasedpaymentsDisclosureofassumptionsusedforthemeasurementofBSAsDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/SharebasedpaymentsDisclosureofassumptionsusedforthemeasurementofBSAsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_a945d3e7-b261-4cc0-bffe-2347aca1e7a3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_3e97a34d-b635-406e-927e-055e2b234f01" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_a945d3e7-b261-4cc0-bffe-2347aca1e7a3" xlink:to="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_3e97a34d-b635-406e-927e-055e2b234f01" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1e07aac0-dadb-4077-9f62-53a9e503aa28" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_3e97a34d-b635-406e-927e-055e2b234f01" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1e07aac0-dadb-4077-9f62-53a9e503aa28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1e07aac0-dadb-4077-9f62-53a9e503aa28_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1e07aac0-dadb-4077-9f62-53a9e503aa28" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1e07aac0-dadb-4077-9f62-53a9e503aa28_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_bd36689e-de41-4630-b393-ac5df24aae67" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1e07aac0-dadb-4077-9f62-53a9e503aa28" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_bd36689e-de41-4630-b393-ac5df24aae67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20241Member_185c4c31-817a-48fd-b512-5e1253949228" xlink:href="abvx-20251231.xsd#abvx_BSA20241Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_bd36689e-de41-4630-b393-ac5df24aae67" xlink:to="loc_abvx_BSA20241Member_185c4c31-817a-48fd-b512-5e1253949228" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20242Member_62ad543a-0251-4574-859f-c7c31f3eae7e" xlink:href="abvx-20251231.xsd#abvx_BSA20242Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_bd36689e-de41-4630-b393-ac5df24aae67" xlink:to="loc_abvx_BSA20242Member_62ad543a-0251-4574-859f-c7c31f3eae7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20251Member_019bfaed-ae59-7133-a193-a5ffe6656b89" xlink:href="abvx-20251231.xsd#abvx_BSA20251Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_bd36689e-de41-4630-b393-ac5df24aae67" xlink:to="loc_abvx_BSA20251Member_019bfaed-ae59-7133-a193-a5ffe6656b89" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20252Member_019bfaed-dcc8-72ca-a67a-612816ceccc1" xlink:href="abvx-20251231.xsd#abvx_BSA20252Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_bd36689e-de41-4630-b393-ac5df24aae67" xlink:to="loc_abvx_BSA20252Member_019bfaed-dcc8-72ca-a67a-612816ceccc1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BSA20253Member_019bfaee-2775-7033-81fd-50d0a3fb96b4" xlink:href="abvx-20251231.xsd#abvx_BSA20253Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_bd36689e-de41-4630-b393-ac5df24aae67" xlink:to="loc_abvx_BSA20253Member_019bfaee-2775-7033-81fd-50d0a3fb96b4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeAxis_8b5c9c89-3de1-4737-bf67-803efd0dc22f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_3e97a34d-b635-406e-927e-055e2b234f01" xlink:to="loc_ifrs-full_RangeAxis_8b5c9c89-3de1-4737-bf67-803efd0dc22f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_8b5c9c89-3de1-4737-bf67-803efd0dc22f_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_RangeAxis_8b5c9c89-3de1-4737-bf67-803efd0dc22f" xlink:to="loc_ifrs-full_RangeDomain_8b5c9c89-3de1-4737-bf67-803efd0dc22f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_508f69b5-53fd-476d-8930-f6027a178b79" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_RangeAxis_8b5c9c89-3de1-4737-bf67-803efd0dc22f" xlink:to="loc_ifrs-full_RangeDomain_508f69b5-53fd-476d-8930-f6027a178b79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_5b9e5b0f-1b3a-4187-bfe9-dfa5291284f7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_508f69b5-53fd-476d-8930-f6027a178b79" xlink:to="loc_srt_MinimumMember_5b9e5b0f-1b3a-4187-bfe9-dfa5291284f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_a839e7dc-4847-40eb-b2f9-1f8d96012b50" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_508f69b5-53fd-476d-8930-f6027a178b79" xlink:to="loc_srt_MaximumMember_a839e7dc-4847-40eb-b2f9-1f8d96012b50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_UnderlyingShareFairValueOtherEquityInstrumentsGranted_f7f75781-682e-4860-9114-6e4726e61e18" xlink:href="abvx-20251231.xsd#abvx_UnderlyingShareFairValueOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_a945d3e7-b261-4cc0-bffe-2347aca1e7a3" xlink:to="loc_abvx_UnderlyingShareFairValueOtherEquityInstrumentsGranted_f7f75781-682e-4860-9114-6e4726e61e18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EquityInstrumentFairValueOtherEquityInstrumentsGranted_be06938d-ea73-414e-a6f1-e25d51f24fee" xlink:href="abvx-20251231.xsd#abvx_EquityInstrumentFairValueOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_a945d3e7-b261-4cc0-bffe-2347aca1e7a3" xlink:to="loc_abvx_EquityInstrumentFairValueOtherEquityInstrumentsGranted_be06938d-ea73-414e-a6f1-e25d51f24fee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_b71452a0-8180-438e-8c53-43b27751e232" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_a945d3e7-b261-4cc0-bffe-2347aca1e7a3" xlink:to="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_b71452a0-8180-438e-8c53-43b27751e232" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EquityInstrumentPriceOtherEquityInstrumentsGranted_6f59ccd3-869f-42d2-be50-a013a34cceb5" xlink:href="abvx-20251231.xsd#abvx_EquityInstrumentPriceOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_a945d3e7-b261-4cc0-bffe-2347aca1e7a3" xlink:to="loc_abvx_EquityInstrumentPriceOtherEquityInstrumentsGranted_6f59ccd3-869f-42d2-be50-a013a34cceb5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EquityInstrumentStrikePriceOtherEquityInstrumentsGranted_9f868d05-8da8-4c05-936e-dc696efbe5ef" xlink:href="abvx-20251231.xsd#abvx_EquityInstrumentStrikePriceOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_a945d3e7-b261-4cc0-bffe-2347aca1e7a3" xlink:to="loc_abvx_EquityInstrumentStrikePriceOtherEquityInstrumentsGranted_9f868d05-8da8-4c05-936e-dc696efbe5ef" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RiskFreeInterestRateOtherEquityInstrumentsGranted_6426209c-6057-46e7-a4bd-2ea7f4528435" xlink:href="abvx-20251231.xsd#abvx_RiskFreeInterestRateOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_a945d3e7-b261-4cc0-bffe-2347aca1e7a3" xlink:to="loc_abvx_RiskFreeInterestRateOtherEquityInstrumentsGranted_6426209c-6057-46e7-a4bd-2ea7f4528435" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExpectedMaturityOtherEquityInstrumentsGranted_701456f7-b201-42c7-83b8-92dc2abf3125" xlink:href="abvx-20251231.xsd#abvx_ExpectedMaturityOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_a945d3e7-b261-4cc0-bffe-2347aca1e7a3" xlink:to="loc_abvx_ExpectedMaturityOtherEquityInstrumentsGranted_701456f7-b201-42c7-83b8-92dc2abf3125" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExpectedVolatilityOtherEquityInstrumentsGranted_69b7111b-bf82-4014-9d5c-bce6e1f15853" xlink:href="abvx-20251231.xsd#abvx_ExpectedVolatilityOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_a945d3e7-b261-4cc0-bffe-2347aca1e7a3" xlink:to="loc_abvx_ExpectedVolatilityOtherEquityInstrumentsGranted_69b7111b-bf82-4014-9d5c-bce6e1f15853" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/SharebasedpaymentsDisclosureofreconciliationofAGAsDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#SharebasedpaymentsDisclosureofreconciliationofAGAsDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/SharebasedpaymentsDisclosureofreconciliationofAGAsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_105b6e0b-1b27-4fb0-8566-495f1a329c4f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_0988986e-9d00-4e8d-bb69-1d92affdd4c1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_105b6e0b-1b27-4fb0-8566-495f1a329c4f" xlink:to="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_0988986e-9d00-4e8d-bb69-1d92affdd4c1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_9cda77e9-331c-42ee-a122-135bb0f2e68f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_0988986e-9d00-4e8d-bb69-1d92affdd4c1" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_9cda77e9-331c-42ee-a122-135bb0f2e68f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_9cda77e9-331c-42ee-a122-135bb0f2e68f_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_9cda77e9-331c-42ee-a122-135bb0f2e68f" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_9cda77e9-331c-42ee-a122-135bb0f2e68f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_3be2ac57-5908-4673-b25d-b24285875322" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_9cda77e9-331c-42ee-a122-135bb0f2e68f" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_3be2ac57-5908-4673-b25d-b24285875322" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:href="abvx-20251231.xsd#abvx_FreeSharesAGAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_3be2ac57-5908-4673-b25d-b24285875322" xlink:to="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20231Member_957c1a0a-a143-4c82-9a37-57da96c03383" xlink:href="abvx-20251231.xsd#abvx_AGA20231Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20231Member_957c1a0a-a143-4c82-9a37-57da96c03383" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20232Member_52aac868-4b55-4cb0-88e3-aee965019447" xlink:href="abvx-20251231.xsd#abvx_AGA20232Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20232Member_52aac868-4b55-4cb0-88e3-aee965019447" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20233Member_e77bc2a4-c84d-4639-bc3f-02bce9b9b2cd" xlink:href="abvx-20251231.xsd#abvx_AGA20233Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20233Member_e77bc2a4-c84d-4639-bc3f-02bce9b9b2cd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20234Member_0dc37682-3285-4975-b9c7-7eb139482202" xlink:href="abvx-20251231.xsd#abvx_AGA20234Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20234Member_0dc37682-3285-4975-b9c7-7eb139482202" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20235Member_14e73a1c-e2ea-4128-92c8-746dec075028" xlink:href="abvx-20251231.xsd#abvx_AGA20235Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20235Member_14e73a1c-e2ea-4128-92c8-746dec075028" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20241Member_2e010280-d2df-43ee-b9fb-07afa98e50b2" xlink:href="abvx-20251231.xsd#abvx_AGA20241Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20241Member_2e010280-d2df-43ee-b9fb-07afa98e50b2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20242Member_d8b97919-4a46-4085-92f1-4ca2dd5549c0" xlink:href="abvx-20251231.xsd#abvx_AGA20242Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20242Member_d8b97919-4a46-4085-92f1-4ca2dd5549c0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20243Member_6cc205c1-7829-4001-9c85-c71f5c80ea9d" xlink:href="abvx-20251231.xsd#abvx_AGA20243Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20243Member_6cc205c1-7829-4001-9c85-c71f5c80ea9d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20244Member_a7114653-b4ec-45af-b8cb-832e22fbbc1a" xlink:href="abvx-20251231.xsd#abvx_AGA20244Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20244Member_a7114653-b4ec-45af-b8cb-832e22fbbc1a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20245Member_15b20233-c70f-4505-8c3d-4f5dee3de02e" xlink:href="abvx-20251231.xsd#abvx_AGA20245Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20245Member_15b20233-c70f-4505-8c3d-4f5dee3de02e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20246Member_a9a9fa34-8e60-4ddc-84f9-3eefce1b95aa" xlink:href="abvx-20251231.xsd#abvx_AGA20246Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20246Member_a9a9fa34-8e60-4ddc-84f9-3eefce1b95aa" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20247Member_ac59c67b-b278-4cf2-ab67-56deb3126df8" xlink:href="abvx-20251231.xsd#abvx_AGA20247Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20247Member_ac59c67b-b278-4cf2-ab67-56deb3126df8" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20251Member_019c5692-5e4c-7297-baf5-0654e9287a2b" xlink:href="abvx-20251231.xsd#abvx_AGA20251Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20251Member_019c5692-5e4c-7297-baf5-0654e9287a2b" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20252Member_019c5692-7d39-7919-bae3-8dc7300f7c9d" xlink:href="abvx-20251231.xsd#abvx_AGA20252Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20252Member_019c5692-7d39-7919-bae3-8dc7300f7c9d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20253Member_019c5693-156e-7d9b-9d8c-0de4c80fa9ba" xlink:href="abvx-20251231.xsd#abvx_AGA20253Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20253Member_019c5693-156e-7d9b-9d8c-0de4c80fa9ba" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20254Member_019c5693-156e-7374-a494-49dc8e97742c" xlink:href="abvx-20251231.xsd#abvx_AGA20254Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20254Member_019c5693-156e-7374-a494-49dc8e97742c" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20255Member_019c5693-156e-78da-ada1-a407ba424dfe" xlink:href="abvx-20251231.xsd#abvx_AGA20255Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20255Member_019c5693-156e-78da-ada1-a407ba424dfe" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20256Member_019c5693-156e-7fd2-8a37-a2204acfd74c" xlink:href="abvx-20251231.xsd#abvx_AGA20256Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20256Member_019c5693-156e-7fd2-8a37-a2204acfd74c" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20257Member_019c5693-156e-751d-8f50-5f3014d2f8c9" xlink:href="abvx-20251231.xsd#abvx_AGA20257Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20257Member_019c5693-156e-751d-8f50-5f3014d2f8c9" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20258Member_019c5693-156e-7f34-977e-59bb5f265164" xlink:href="abvx-20251231.xsd#abvx_AGA20258Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FreeSharesAGAMember_959f8758-fa1b-43c1-854c-b8efc69ad91a" xlink:to="loc_abvx_AGA20258Member_019c5693-156e-7f34-977e-59bb5f265164" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement_04363a92-f910-4196-aecf-cd3887bea24f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_105b6e0b-1b27-4fb0-8566-495f1a329c4f" xlink:to="loc_ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement_04363a92-f910-4196-aecf-cd3887bea24f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_e0da9dc1-b61d-47a8-850e-20e42cdb9f1d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_105b6e0b-1b27-4fb0-8566-495f1a329c4f" xlink:to="loc_ifrs-full_NumberOfInstrumentsOtherEquityInstrumentsGranted_e0da9dc1-b61d-47a8-850e-20e42cdb9f1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfOtherEquityInstrumentsExpiredInSharebasedPaymentArrangement_dfd0361b-c554-414c-a29b-195905bb5a39" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfOtherEquityInstrumentsExpiredInSharebasedPaymentArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_105b6e0b-1b27-4fb0-8566-495f1a329c4f" xlink:to="loc_ifrs-full_NumberOfOtherEquityInstrumentsExpiredInSharebasedPaymentArrangement_dfd0361b-c554-414c-a29b-195905bb5a39" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfOtherEquityInstrumentsExercisedOrVestedInSharebasedPaymentArrangement_eccaf176-0d8d-431f-aac1-9b93b99accb7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfOtherEquityInstrumentsExercisedOrVestedInSharebasedPaymentArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_105b6e0b-1b27-4fb0-8566-495f1a329c4f" xlink:to="loc_ifrs-full_NumberOfOtherEquityInstrumentsExercisedOrVestedInSharebasedPaymentArrangement_eccaf176-0d8d-431f-aac1-9b93b99accb7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement_9aa5df59-22c1-40db-a46c-399a1f95a467" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/SharebasedpaymentsDisclosureofassumptionsusedforthemeasurementofAGAsDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#SharebasedpaymentsDisclosureofassumptionsusedforthemeasurementofAGAsDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/SharebasedpaymentsDisclosureofassumptionsusedforthemeasurementofAGAsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_b3ca2a2e-c90d-4d1c-9bf9-de9711b84c9f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_e440733e-c619-46da-a594-be39ed72163e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_b3ca2a2e-c90d-4d1c-9bf9-de9711b84c9f" xlink:to="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_e440733e-c619-46da-a594-be39ed72163e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_6c6b36a4-23ff-4291-8831-1f50fc2b09d1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_e440733e-c619-46da-a594-be39ed72163e" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_6c6b36a4-23ff-4291-8831-1f50fc2b09d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_6c6b36a4-23ff-4291-8831-1f50fc2b09d1_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_6c6b36a4-23ff-4291-8831-1f50fc2b09d1" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_6c6b36a4-23ff-4291-8831-1f50fc2b09d1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_6c6b36a4-23ff-4291-8831-1f50fc2b09d1" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20231Member_49dafe01-6f1b-4ba7-bbb6-1313ad94c7a4" xlink:href="abvx-20251231.xsd#abvx_AGA20231Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20231Member_49dafe01-6f1b-4ba7-bbb6-1313ad94c7a4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20232Member_839267f9-4505-48d0-811a-45d21184c399" xlink:href="abvx-20251231.xsd#abvx_AGA20232Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20232Member_839267f9-4505-48d0-811a-45d21184c399" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20233Member_f4224785-3a69-4c35-8fe6-5cfc54420e8f" xlink:href="abvx-20251231.xsd#abvx_AGA20233Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20233Member_f4224785-3a69-4c35-8fe6-5cfc54420e8f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20234Member_f220248a-fa96-4f48-a67d-0cc088f48ef4" xlink:href="abvx-20251231.xsd#abvx_AGA20234Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20234Member_f220248a-fa96-4f48-a67d-0cc088f48ef4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20235Member_faf3ace0-28cc-457a-a848-121969810a84" xlink:href="abvx-20251231.xsd#abvx_AGA20235Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20235Member_faf3ace0-28cc-457a-a848-121969810a84" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20241Member_22cec87c-bfbf-457f-9fbc-44ac368a9153" xlink:href="abvx-20251231.xsd#abvx_AGA20241Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20241Member_22cec87c-bfbf-457f-9fbc-44ac368a9153" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20242Member_df90699a-2710-4cb6-be44-871c7e55b255" xlink:href="abvx-20251231.xsd#abvx_AGA20242Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20242Member_df90699a-2710-4cb6-be44-871c7e55b255" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20243Member_551d2e37-2680-4485-a76a-880d6faf8edb" xlink:href="abvx-20251231.xsd#abvx_AGA20243Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20243Member_551d2e37-2680-4485-a76a-880d6faf8edb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20244Member_d449e3a6-b423-4c0a-9c8d-05d898e96827" xlink:href="abvx-20251231.xsd#abvx_AGA20244Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20244Member_d449e3a6-b423-4c0a-9c8d-05d898e96827" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20245Member_c2a480d6-0052-48d7-a6f6-7cba92444f98" xlink:href="abvx-20251231.xsd#abvx_AGA20245Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20245Member_c2a480d6-0052-48d7-a6f6-7cba92444f98" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20246Member_32d88de7-36ec-42b2-a6a4-808afe736443" xlink:href="abvx-20251231.xsd#abvx_AGA20246Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20246Member_32d88de7-36ec-42b2-a6a4-808afe736443" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20247Member_f9fad285-039d-41d3-8369-a1525e64d368" xlink:href="abvx-20251231.xsd#abvx_AGA20247Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20247Member_f9fad285-039d-41d3-8369-a1525e64d368" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20251Member_019bfaf5-15ee-7c3c-b433-8a2d55bcbccd" xlink:href="abvx-20251231.xsd#abvx_AGA20251Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20251Member_019bfaf5-15ee-7c3c-b433-8a2d55bcbccd" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20252Member_019bfaf5-3a27-743f-9e7d-76c284967e3a" xlink:href="abvx-20251231.xsd#abvx_AGA20252Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20252Member_019bfaf5-3a27-743f-9e7d-76c284967e3a" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20253Member_019bfaf6-28ef-7590-8b1c-8564f1c3a08d" xlink:href="abvx-20251231.xsd#abvx_AGA20253Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20253Member_019bfaf6-28ef-7590-8b1c-8564f1c3a08d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20254Member_019bfaf6-508e-7cd4-9c2d-9bd58109086d" xlink:href="abvx-20251231.xsd#abvx_AGA20254Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20254Member_019bfaf6-508e-7cd4-9c2d-9bd58109086d" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20255Member_019bfaf6-6be7-7b43-8199-263a9a99589d" xlink:href="abvx-20251231.xsd#abvx_AGA20255Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20255Member_019bfaf6-6be7-7b43-8199-263a9a99589d" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20256Member_019bfaf7-9523-7304-bde2-53ff6d310451" xlink:href="abvx-20251231.xsd#abvx_AGA20256Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20256Member_019bfaf7-9523-7304-bde2-53ff6d310451" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20257Member_019bfaf7-c34f-791b-b82a-5318dc0e92b5" xlink:href="abvx-20251231.xsd#abvx_AGA20257Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20257Member_019bfaf7-c34f-791b-b82a-5318dc0e92b5" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AGA20258Member_019bfaf7-ee30-75cd-a998-17888b5d557b" xlink:href="abvx-20251231.xsd#abvx_AGA20258Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_989786a7-0a3e-4ad1-a9f6-8a77d006dbc7" xlink:to="loc_abvx_AGA20258Member_019bfaf7-ee30-75cd-a998-17888b5d557b" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesAxis_09b7b9df-4e33-40b6-8a8a-6657b6fa0ef1" xlink:href="abvx-20251231.xsd#abvx_TranchesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_e440733e-c619-46da-a594-be39ed72163e" xlink:to="loc_abvx_TranchesAxis_09b7b9df-4e33-40b6-8a8a-6657b6fa0ef1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesDomain_09b7b9df-4e33-40b6-8a8a-6657b6fa0ef1_default" xlink:href="abvx-20251231.xsd#abvx_TranchesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_TranchesAxis_09b7b9df-4e33-40b6-8a8a-6657b6fa0ef1" xlink:to="loc_abvx_TranchesDomain_09b7b9df-4e33-40b6-8a8a-6657b6fa0ef1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesDomain_3de17878-cffd-468d-a372-d10fd82267dd" xlink:href="abvx-20251231.xsd#abvx_TranchesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_TranchesAxis_09b7b9df-4e33-40b6-8a8a-6657b6fa0ef1" xlink:to="loc_abvx_TranchesDomain_3de17878-cffd-468d-a372-d10fd82267dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesOneToFourMember_be82ef3d-f04e-4ee5-a585-82d5aca8125e" xlink:href="abvx-20251231.xsd#abvx_TranchesOneToFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_3de17878-cffd-468d-a372-d10fd82267dd" xlink:to="loc_abvx_TranchesOneToFourMember_be82ef3d-f04e-4ee5-a585-82d5aca8125e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheFiveMember_9f707d3c-f0ab-49c7-9a5f-01126d97dde8" xlink:href="abvx-20251231.xsd#abvx_TrancheFiveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_3de17878-cffd-468d-a372-d10fd82267dd" xlink:to="loc_abvx_TrancheFiveMember_9f707d3c-f0ab-49c7-9a5f-01126d97dde8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheSixMember_d1f95c06-03f8-4b3c-a2a2-c73fe949d771" xlink:href="abvx-20251231.xsd#abvx_TrancheSixMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_3de17878-cffd-468d-a372-d10fd82267dd" xlink:to="loc_abvx_TrancheSixMember_d1f95c06-03f8-4b3c-a2a2-c73fe949d771" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheOneMember_827db1be-c912-4b8b-8ab6-b6af511af08e" xlink:href="abvx-20251231.xsd#abvx_TrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_3de17878-cffd-468d-a372-d10fd82267dd" xlink:to="loc_abvx_TrancheOneMember_827db1be-c912-4b8b-8ab6-b6af511af08e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheTwoMember_7a1bcec3-926d-4231-b5e7-513d6fc81ac8" xlink:href="abvx-20251231.xsd#abvx_TrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_3de17878-cffd-468d-a372-d10fd82267dd" xlink:to="loc_abvx_TrancheTwoMember_7a1bcec3-926d-4231-b5e7-513d6fc81ac8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_UnderlyingShareFairValueOtherEquityInstrumentsGranted_0c990f3d-cc1b-4596-a2bb-a502430bef02" xlink:href="abvx-20251231.xsd#abvx_UnderlyingShareFairValueOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_b3ca2a2e-c90d-4d1c-9bf9-de9711b84c9f" xlink:to="loc_abvx_UnderlyingShareFairValueOtherEquityInstrumentsGranted_0c990f3d-cc1b-4596-a2bb-a502430bef02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EquityInstrumentFairValueOtherEquityInstrumentsGranted_0aeaf74b-20e8-4115-9e2c-7338fea6bc5b" xlink:href="abvx-20251231.xsd#abvx_EquityInstrumentFairValueOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_b3ca2a2e-c90d-4d1c-9bf9-de9711b84c9f" xlink:to="loc_abvx_EquityInstrumentFairValueOtherEquityInstrumentsGranted_0aeaf74b-20e8-4115-9e2c-7338fea6bc5b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EquityInstrumentPriceOtherEquityInstrumentsGranted_43227f63-d871-4b05-9d00-5ad12f8d7d80" xlink:href="abvx-20251231.xsd#abvx_EquityInstrumentPriceOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_b3ca2a2e-c90d-4d1c-9bf9-de9711b84c9f" xlink:to="loc_abvx_EquityInstrumentPriceOtherEquityInstrumentsGranted_43227f63-d871-4b05-9d00-5ad12f8d7d80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExpectedVolatilityOtherEquityInstrumentsGranted_01aa0598-f4a7-4117-819b-2b397fb0f248" xlink:href="abvx-20251231.xsd#abvx_ExpectedVolatilityOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_b3ca2a2e-c90d-4d1c-9bf9-de9711b84c9f" xlink:to="loc_abvx_ExpectedVolatilityOtherEquityInstrumentsGranted_01aa0598-f4a7-4117-819b-2b397fb0f248" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RiskFreeInterestRateOtherEquityInstrumentsGranted_1534f37d-db18-44c8-8fa5-8793f15a2ca0" xlink:href="abvx-20251231.xsd#abvx_RiskFreeInterestRateOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_b3ca2a2e-c90d-4d1c-9bf9-de9711b84c9f" xlink:to="loc_abvx_RiskFreeInterestRateOtherEquityInstrumentsGranted_1534f37d-db18-44c8-8fa5-8793f15a2ca0" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/SharebasedpaymentsDisclosureofbreakdownofthecompensationexpensesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#SharebasedpaymentsDisclosureofbreakdownofthecompensationexpensesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/SharebasedpaymentsDisclosureofbreakdownofthecompensationexpensesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_3be04068-1f23-42a2-ab9e-a0bc2b5c7cf0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_822bc12a-13be-4a39-bfff-1a841397c162" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_3be04068-1f23-42a2-ab9e-a0bc2b5c7cf0" xlink:to="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_822bc12a-13be-4a39-bfff-1a841397c162" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_e67d9f5f-1c2d-4626-91aa-ab6319e8c3c2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable_822bc12a-13be-4a39-bfff-1a841397c162" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_e67d9f5f-1c2d-4626-91aa-ab6319e8c3c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_e67d9f5f-1c2d-4626-91aa-ab6319e8c3c2_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_e67d9f5f-1c2d-4626-91aa-ab6319e8c3c2" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_e67d9f5f-1c2d-4626-91aa-ab6319e8c3c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_16980579-7140-49dd-b956-4701d3b58e5e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_e67d9f5f-1c2d-4626-91aa-ab6319e8c3c2" xlink:to="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_16980579-7140-49dd-b956-4701d3b58e5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_adf84893-6f18-4db4-9941-563d31e999ed" xlink:href="abvx-20251231.xsd#abvx_FoundersShareSubscriptionWarrantsBCEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_16980579-7140-49dd-b956-4701d3b58e5e" xlink:to="loc_abvx_FoundersShareSubscriptionWarrantsBCEMember_adf84893-6f18-4db4-9941-563d31e999ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ShareSubscriptionWarrantsBSAMember_72c50e5e-f9fb-41b1-aa6f-b8097494c77e" xlink:href="abvx-20251231.xsd#abvx_ShareSubscriptionWarrantsBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_16980579-7140-49dd-b956-4701d3b58e5e" xlink:to="loc_abvx_ShareSubscriptionWarrantsBSAMember_72c50e5e-f9fb-41b1-aa6f-b8097494c77e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FreeSharesAGAMember_285603fd-4072-4769-bbda-ec66366d383f" xlink:href="abvx-20251231.xsd#abvx_FreeSharesAGAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_16980579-7140-49dd-b956-4701d3b58e5e" xlink:to="loc_abvx_FreeSharesAGAMember_285603fd-4072-4769-bbda-ec66366d383f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ExpenseFromEquitysettledSharebasedPaymentTransactionsInWhichGoodsOrServicesReceivedDidNotQualifyForRecognitionAsAssets_8fb6c5d8-17a0-4a80-9776-679994e3c0f2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ExpenseFromEquitysettledSharebasedPaymentTransactionsInWhichGoodsOrServicesReceivedDidNotQualifyForRecognitionAsAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_3be04068-1f23-42a2-ab9e-a0bc2b5c7cf0" xlink:to="loc_ifrs-full_ExpenseFromEquitysettledSharebasedPaymentTransactionsInWhichGoodsOrServicesReceivedDidNotQualifyForRecognitionAsAssets_8fb6c5d8-17a0-4a80-9776-679994e3c0f2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExpenseFromEquitySettledShareBasedPaymentTransactionsSocialTaxes_8b5629ba-1a6b-453a-a173-01547b2fbc0e" xlink:href="abvx-20251231.xsd#abvx_ExpenseFromEquitySettledShareBasedPaymentTransactionsSocialTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_3be04068-1f23-42a2-ab9e-a0bc2b5c7cf0" xlink:to="loc_abvx_ExpenseFromEquitySettledShareBasedPaymentTransactionsSocialTaxes_8b5629ba-1a6b-453a-a173-01547b2fbc0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ExpenseFromSharebasedPaymentTransactionsInWhichGoodsOrServicesReceivedDidNotQualifyForRecognitionAsAssets_39f7dc0f-4999-4436-8806-49f07908940a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ExpenseFromSharebasedPaymentTransactionsInWhichGoodsOrServicesReceivedDidNotQualifyForRecognitionAsAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_3be04068-1f23-42a2-ab9e-a0bc2b5c7cf0" xlink:to="loc_ifrs-full_ExpenseFromSharebasedPaymentTransactionsInWhichGoodsOrServicesReceivedDidNotQualifyForRecognitionAsAssets_39f7dc0f-4999-4436-8806-49f07908940a" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesDisclosureoffinancialliabilitiesbreakdownDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesDisclosureoffinancialliabilitiesbreakdownDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesDisclosureoffinancialliabilitiesbreakdownDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_f988ba67-7836-40ed-804f-c775cc9451ae" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_b4ca613f-d6b8-42d9-a4a1-381e6b751182" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_f988ba67-7836-40ed-804f-c775cc9451ae" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_b4ca613f-d6b8-42d9-a4a1-381e6b751182" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_3c062d8d-0f33-4a06-84fc-c32d7757ebc5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_b4ca613f-d6b8-42d9-a4a1-381e6b751182" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_3c062d8d-0f33-4a06-84fc-c32d7757ebc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_3c062d8d-0f33-4a06-84fc-c32d7757ebc5_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_3c062d8d-0f33-4a06-84fc-c32d7757ebc5" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_3c062d8d-0f33-4a06-84fc-c32d7757ebc5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_8164547c-f892-4c72-ac89-3660ffe4a95b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_3c062d8d-0f33-4a06-84fc-c32d7757ebc5" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_8164547c-f892-4c72-ac89-3660ffe4a95b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Borrowings1Member_32df8845-b5b8-472e-a979-f0a5fd829e54" xlink:href="abvx-20251231.xsd#abvx_Borrowings1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_8164547c-f892-4c72-ac89-3660ffe4a95b" xlink:to="loc_abvx_Borrowings1Member_32df8845-b5b8-472e-a979-f0a5fd829e54" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos1ClaretBondLoansMember_842e9057-8a21-46d3-8bb6-e13732adea47" xlink:href="abvx-20251231.xsd#abvx_Kreos1ClaretBondLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_Borrowings1Member_32df8845-b5b8-472e-a979-f0a5fd829e54" xlink:to="loc_abvx_Kreos1ClaretBondLoansMember_842e9057-8a21-46d3-8bb6-e13732adea47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LeaseLiabilitiesMember_ec3ee55c-1b57-4ca3-ad52-1b7db5eabef5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LeaseLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_Borrowings1Member_32df8845-b5b8-472e-a979-f0a5fd829e54" xlink:to="loc_ifrs-full_LeaseLiabilitiesMember_ec3ee55c-1b57-4ca3-ad52-1b7db5eabef5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PretGarantiParLEtatPGEMember_270cae6d-821f-4510-b3d0-df1b51677dda" xlink:href="abvx-20251231.xsd#abvx_PretGarantiParLEtatPGEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_Borrowings1Member_32df8845-b5b8-472e-a979-f0a5fd829e54" xlink:to="loc_abvx_PretGarantiParLEtatPGEMember_270cae6d-821f-4510-b3d0-df1b51677dda" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConvertibleLoansNotesMember_8cf103b1-8abd-437b-93c8-eb0dc18deb30" xlink:href="abvx-20251231.xsd#abvx_ConvertibleLoansNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_8164547c-f892-4c72-ac89-3660ffe4a95b" xlink:to="loc_abvx_ConvertibleLoansNotesMember_8cf103b1-8abd-437b-93c8-eb0dc18deb30" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheAMember_288d002c-69e3-4117-ad71-56c015eeb977" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ConvertibleLoansNotesMember_8cf103b1-8abd-437b-93c8-eb0dc18deb30" xlink:to="loc_abvx_KreosClaretFinancingTrancheAMember_288d002c-69e3-4117-ad71-56c015eeb977" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_HeightsConvertibleNotesMember_2b2cb042-56a2-4b43-ba7f-5042cb4e99b6" xlink:href="abvx-20251231.xsd#abvx_HeightsConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_ConvertibleLoansNotesMember_8cf103b1-8abd-437b-93c8-eb0dc18deb30" xlink:to="loc_abvx_HeightsConvertibleNotesMember_2b2cb042-56a2-4b43-ba7f-5042cb4e99b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DerivativesMember_e378ff87-67ef-4be6-b035-dc1671b48702" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DerivativesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_8164547c-f892-4c72-ac89-3660ffe4a95b" xlink:to="loc_ifrs-full_DerivativesMember_e378ff87-67ef-4be6-b035-dc1671b48702" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretMinimumReturnIndemnificationsMember_6156b6c6-61cb-4c6c-b8ae-7a6beb8b6818" xlink:href="abvx-20251231.xsd#abvx_KreosClaretMinimumReturnIndemnificationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DerivativesMember_e378ff87-67ef-4be6-b035-dc1671b48702" xlink:to="loc_abvx_KreosClaretMinimumReturnIndemnificationsMember_6156b6c6-61cb-4c6c-b8ae-7a6beb8b6818" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingBSAMember_8a156ce0-2b52-4d12-818a-641f5e60375a" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DerivativesMember_e378ff87-67ef-4be6-b035-dc1671b48702" xlink:to="loc_abvx_KreosClaretFinancingBSAMember_8a156ce0-2b52-4d12-818a-641f5e60375a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherFinancialLiabilitiesMember_f98bd28e-99e2-4080-b110-4b53bbb21327" xlink:href="abvx-20251231.xsd#abvx_OtherFinancialLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_8164547c-f892-4c72-ac89-3660ffe4a95b" xlink:to="loc_abvx_OtherFinancialLiabilitiesMember_f98bd28e-99e2-4080-b110-4b53bbb21327" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConditionalAdvancesMember_170b5755-c9d8-4c51-bb5b-60de31a6195d" xlink:href="abvx-20251231.xsd#abvx_ConditionalAdvancesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_OtherFinancialLiabilitiesMember_f98bd28e-99e2-4080-b110-4b53bbb21327" xlink:to="loc_abvx_ConditionalAdvancesMember_170b5755-c9d8-4c51-bb5b-60de31a6195d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RoyaltyCertificatesMember_3d29cb2b-7ec9-40f9-bfc9-f1c473ff024b" xlink:href="abvx-20251231.xsd#abvx_RoyaltyCertificatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_OtherFinancialLiabilitiesMember_f98bd28e-99e2-4080-b110-4b53bbb21327" xlink:to="loc_abvx_RoyaltyCertificatesMember_3d29cb2b-7ec9-40f9-bfc9-f1c473ff024b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NoncurrentFinancialLiabilities_5ad64c42-5834-415e-be80-b3ecc28bc68b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NoncurrentFinancialLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_f988ba67-7836-40ed-804f-c775cc9451ae" xlink:to="loc_ifrs-full_NoncurrentFinancialLiabilities_5ad64c42-5834-415e-be80-b3ecc28bc68b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CurrentFinancialLiabilities_2209f43e-e657-4cd6-b302-86bb3e0ca748" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CurrentFinancialLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_f988ba67-7836-40ed-804f-c775cc9451ae" xlink:to="loc_ifrs-full_CurrentFinancialLiabilities_2209f43e-e657-4cd6-b302-86bb3e0ca748" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_FinancialLiabilities_a2efd26d-f298-4fa2-a282-9bb9549aa3ae" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FinancialLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_f988ba67-7836-40ed-804f-c775cc9451ae" xlink:to="loc_ifrs-full_FinancialLiabilities_a2efd26d-f298-4fa2-a282-9bb9549aa3ae" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesKreosClaretFinancingDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesKreosClaretFinancingDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesKreosClaretFinancingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_2d725804-2b58-4529-b3a8-ded122e8fe7d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_2d725804-2b58-4529-b3a8-ded122e8fe7d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_019bfefd-f0b7-71e3-8e09-e45b9e1155a9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_2d725804-2b58-4529-b3a8-ded122e8fe7d" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_019bfefd-f0b7-71e3-8e09-e45b9e1155a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019bfefd-f0b7-71e3-8e09-e45b9e1155a9_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019bfefd-f0b7-71e3-8e09-e45b9e1155a9" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019bfefd-f0b7-71e3-8e09-e45b9e1155a9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019bfefd-f0b7-7397-a01e-9c0fb982c54a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019bfefd-f0b7-71e3-8e09-e45b9e1155a9" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019bfefd-f0b7-7397-a01e-9c0fb982c54a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingMember_019bfefd-f0b7-7391-bf9a-cd0f45659582" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bfefd-f0b7-7397-a01e-9c0fb982c54a" xlink:to="loc_abvx_KreosClaretFinancingMember_019bfefd-f0b7-7391-bf9a-cd0f45659582" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheAMember_019bfefe-190c-72bd-9735-f8ac34d3c33b" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bfefd-f0b7-7397-a01e-9c0fb982c54a" xlink:to="loc_abvx_KreosClaretFinancingTrancheAMember_019bfefe-190c-72bd-9735-f8ac34d3c33b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheBMember_019bfefe-58cf-70b4-a0cd-d87c56d2329d" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bfefd-f0b7-7397-a01e-9c0fb982c54a" xlink:to="loc_abvx_KreosClaretFinancingTrancheBMember_019bfefe-58cf-70b4-a0cd-d87c56d2329d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheCMember_019bfefe-58cf-7759-bb29-652ca1ad0273" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bfefd-f0b7-7397-a01e-9c0fb982c54a" xlink:to="loc_abvx_KreosClaretFinancingTrancheCMember_019bfefe-58cf-7759-bb29-652ca1ad0273" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingSeniorSecuredNonConvertibleLoansMember_019bfefe-58cf-7f61-bbc3-9c0c638dfd0b" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingSeniorSecuredNonConvertibleLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bfefd-f0b7-7397-a01e-9c0fb982c54a" xlink:to="loc_abvx_KreosClaretFinancingSeniorSecuredNonConvertibleLoansMember_019bfefe-58cf-7f61-bbc3-9c0c638dfd0b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos1BondLoansMember_019bfefe-b216-7a7a-8ea8-066bc2005562" xlink:href="abvx-20251231.xsd#abvx_Kreos1BondLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bfefd-f0b7-7397-a01e-9c0fb982c54a" xlink:to="loc_abvx_Kreos1BondLoansMember_019bfefe-b216-7a7a-8ea8-066bc2005562" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosABCBSAMember_019bfefe-d819-729b-a6a4-002f3b950783" xlink:href="abvx-20251231.xsd#abvx_KreosABCBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bfefd-f0b7-7397-a01e-9c0fb982c54a" xlink:to="loc_abvx_KreosABCBSAMember_019bfefe-d819-729b-a6a4-002f3b950783" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingBAndCMember_019c56b3-373e-76b3-9eef-e54272a17ad2" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingBAndCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bfefd-f0b7-7397-a01e-9c0fb982c54a" xlink:to="loc_abvx_KreosClaretFinancingBAndCMember_019c56b3-373e-76b3-9eef-e54272a17ad2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfInterestRatesAxis_019bfefe-58cf-796a-bda2-c3981ef6873f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfInterestRatesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_2d725804-2b58-4529-b3a8-ded122e8fe7d" xlink:to="loc_ifrs-full_TypesOfInterestRatesAxis_019bfefe-58cf-796a-bda2-c3981ef6873f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfInterestRatesDomain_019bfefe-58cf-796a-bda2-c3981ef6873f_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfInterestRatesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfInterestRatesAxis_019bfefe-58cf-796a-bda2-c3981ef6873f" xlink:to="loc_ifrs-full_TypesOfInterestRatesDomain_019bfefe-58cf-796a-bda2-c3981ef6873f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfInterestRatesDomain_019bfefe-58cf-7677-aacc-088b4ee88027" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfInterestRatesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfInterestRatesAxis_019bfefe-58cf-796a-bda2-c3981ef6873f" xlink:to="loc_ifrs-full_TypesOfInterestRatesDomain_019bfefe-58cf-7677-aacc-088b4ee88027" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EuropeanCentralBankBaseRateMember_019bfefe-58cf-70c0-a40e-616974249b76" xlink:href="abvx-20251231.xsd#abvx_EuropeanCentralBankBaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfInterestRatesDomain_019bfefe-58cf-7677-aacc-088b4ee88027" xlink:to="loc_abvx_EuropeanCentralBankBaseRateMember_019bfefe-58cf-70c0-a40e-616974249b76" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeAxis_019bfefe-58cf-79af-a4de-c092ef8acb89" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_2d725804-2b58-4529-b3a8-ded122e8fe7d" xlink:to="loc_ifrs-full_RangeAxis_019bfefe-58cf-79af-a4de-c092ef8acb89" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_019bfefe-58cf-79af-a4de-c092ef8acb89_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_RangeAxis_019bfefe-58cf-79af-a4de-c092ef8acb89" xlink:to="loc_ifrs-full_RangeDomain_019bfefe-58cf-79af-a4de-c092ef8acb89_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_019bfefe-58cf-72e6-ad11-9a7e73d10db2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_RangeAxis_019bfefe-58cf-79af-a4de-c092ef8acb89" xlink:to="loc_ifrs-full_RangeDomain_019bfefe-58cf-72e6-ad11-9a7e73d10db2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BottomOfRangeMember_019bfefe-58cf-7af5-bfa9-8750052b5593" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BottomOfRangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_019bfefe-58cf-72e6-ad11-9a7e73d10db2" xlink:to="loc_ifrs-full_BottomOfRangeMember_019bfefe-58cf-7af5-bfa9-8750052b5593" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TopOfRangeMember_019bfefe-58cf-7caf-95ab-e480c33f258a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TopOfRangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_019bfefe-58cf-72e6-ad11-9a7e73d10db2" xlink:to="loc_ifrs-full_TopOfRangeMember_019bfefe-58cf-7caf-95ab-e480c33f258a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsAxis_019bfefe-b216-7673-bdca-49cc018560d8" xlink:href="abvx-20251231.xsd#abvx_WarrantsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_2d725804-2b58-4529-b3a8-ded122e8fe7d" xlink:to="loc_abvx_WarrantsAxis_019bfefe-b216-7673-bdca-49cc018560d8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsDomain_019bfefe-b216-7673-bdca-49cc018560d8_default" xlink:href="abvx-20251231.xsd#abvx_WarrantsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_WarrantsAxis_019bfefe-b216-7673-bdca-49cc018560d8" xlink:to="loc_abvx_WarrantsDomain_019bfefe-b216-7673-bdca-49cc018560d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsDomain_019bfefe-b216-7d04-9853-b555dccd1d3a" xlink:href="abvx-20251231.xsd#abvx_WarrantsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_WarrantsAxis_019bfefe-b216-7673-bdca-49cc018560d8" xlink:to="loc_abvx_WarrantsDomain_019bfefe-b216-7d04-9853-b555dccd1d3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosABBSAMember_019bfefe-b216-7699-ae9b-f37c49e2ebf7" xlink:href="abvx-20251231.xsd#abvx_KreosABBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_WarrantsDomain_019bfefe-b216-7d04-9853-b555dccd1d3a" xlink:to="loc_abvx_KreosABBSAMember_019bfefe-b216-7699-ae9b-f37c49e2ebf7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosCBSAMember_019bfefe-b216-71cc-93a4-d4e15399dacc" xlink:href="abvx-20251231.xsd#abvx_KreosCBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_WarrantsDomain_019bfefe-b216-7d04-9853-b555dccd1d3a" xlink:to="loc_abvx_KreosCBSAMember_019bfefe-b216-71cc-93a4-d4e15399dacc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosABCBSAMember_019bff0c-e052-7dbd-b0f9-89eb141b253e" xlink:href="abvx-20251231.xsd#abvx_KreosABCBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_WarrantsDomain_019bfefe-b216-7d04-9853-b555dccd1d3a" xlink:to="loc_abvx_KreosABCBSAMember_019bff0c-e052-7dbd-b0f9-89eb141b253e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalAxis_019bfefe-d819-7682-8ce4-1914ffc84f44" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_2d725804-2b58-4529-b3a8-ded122e8fe7d" xlink:to="loc_ifrs-full_ClassesOfShareCapitalAxis_019bfefe-d819-7682-8ce4-1914ffc84f44" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalDomain_019bfefe-d819-7682-8ce4-1914ffc84f44_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfShareCapitalAxis_019bfefe-d819-7682-8ce4-1914ffc84f44" xlink:to="loc_ifrs-full_ClassesOfShareCapitalDomain_019bfefe-d819-7682-8ce4-1914ffc84f44_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalDomain_019bfefe-d819-749d-837f-1fc3f9a2df8b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfShareCapitalAxis_019bfefe-d819-7682-8ce4-1914ffc84f44" xlink:to="loc_ifrs-full_ClassesOfShareCapitalDomain_019bfefe-d819-749d-837f-1fc3f9a2df8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OrdinarySharesMember_019bfefe-d819-751f-a0bb-1685db38888c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfShareCapitalDomain_019bfefe-d819-749d-837f-1fc3f9a2df8b" xlink:to="loc_ifrs-full_OrdinarySharesMember_019bfefe-d819-751f-a0bb-1685db38888c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialAgreementAxis_019bfefe-d819-70bc-8553-91dd2e61485f" xlink:href="abvx-20251231.xsd#abvx_FinancialAgreementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_2d725804-2b58-4529-b3a8-ded122e8fe7d" xlink:to="loc_abvx_FinancialAgreementAxis_019bfefe-d819-70bc-8553-91dd2e61485f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialAgreementDomain_019bfefe-d819-70bc-8553-91dd2e61485f_default" xlink:href="abvx-20251231.xsd#abvx_FinancialAgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_FinancialAgreementAxis_019bfefe-d819-70bc-8553-91dd2e61485f" xlink:to="loc_abvx_FinancialAgreementDomain_019bfefe-d819-70bc-8553-91dd2e61485f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialAgreementDomain_019bfefe-d819-7ca6-bcb1-1d318ea29161" xlink:href="abvx-20251231.xsd#abvx_FinancialAgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_FinancialAgreementAxis_019bfefe-d819-70bc-8553-91dd2e61485f" xlink:to="loc_abvx_FinancialAgreementDomain_019bfefe-d819-7ca6-bcb1-1d318ea29161" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingMember_019bff03-0eb3-7320-89fe-3b4cb0b9edab" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_FinancialAgreementDomain_019bfefe-d819-7ca6-bcb1-1d318ea29161" xlink:to="loc_abvx_KreosClaretFinancingMember_019bff03-0eb3-7320-89fe-3b4cb0b9edab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesAxis_019bfeff-00b5-72ed-9122-7bef7f97b596" xlink:href="abvx-20251231.xsd#abvx_TranchesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_2d725804-2b58-4529-b3a8-ded122e8fe7d" xlink:to="loc_abvx_TranchesAxis_019bfeff-00b5-72ed-9122-7bef7f97b596" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesDomain_019bfeff-00b5-72ed-9122-7bef7f97b596_default" xlink:href="abvx-20251231.xsd#abvx_TranchesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_TranchesAxis_019bfeff-00b5-72ed-9122-7bef7f97b596" xlink:to="loc_abvx_TranchesDomain_019bfeff-00b5-72ed-9122-7bef7f97b596_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesDomain_019bfeff-00b5-76de-a855-2d9bc1d77a55" xlink:href="abvx-20251231.xsd#abvx_TranchesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_TranchesAxis_019bfeff-00b5-72ed-9122-7bef7f97b596" xlink:to="loc_abvx_TranchesDomain_019bfeff-00b5-76de-a855-2d9bc1d77a55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheABAndCMember_019bfeff-00b5-78fd-9345-78ebef8844a2" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheABAndCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_019bfeff-00b5-76de-a855-2d9bc1d77a55" xlink:to="loc_abvx_KreosClaretFinancingTrancheABAndCMember_019bfeff-00b5-78fd-9345-78ebef8844a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfLiabilitiesAxis_019bfeff-00b5-7080-be53-dcd7dac7f3c9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_2d725804-2b58-4529-b3a8-ded122e8fe7d" xlink:to="loc_ifrs-full_ClassesOfLiabilitiesAxis_019bfeff-00b5-7080-be53-dcd7dac7f3c9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfLiabilitiesDomain_019bfeff-00b5-7080-be53-dcd7dac7f3c9_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesAxis_019bfeff-00b5-7080-be53-dcd7dac7f3c9" xlink:to="loc_ifrs-full_ClassesOfLiabilitiesDomain_019bfeff-00b5-7080-be53-dcd7dac7f3c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfLiabilitiesDomain_019bfeff-00b5-72d4-ad89-08d6cad5c0a6" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesAxis_019bfeff-00b5-7080-be53-dcd7dac7f3c9" xlink:to="loc_ifrs-full_ClassesOfLiabilitiesDomain_019bfeff-00b5-72d4-ad89-08d6cad5c0a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretMinimumReturnIndemnificationsMember_019bfeff-00b5-7247-b73a-3e32e6de1bf5" xlink:href="abvx-20251231.xsd#abvx_KreosClaretMinimumReturnIndemnificationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesDomain_019bfeff-00b5-72d4-ad89-08d6cad5c0a6" xlink:to="loc_abvx_KreosClaretMinimumReturnIndemnificationsMember_019bfeff-00b5-7247-b73a-3e32e6de1bf5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019bfeff-82d5-7a4c-8385-489519e6b09f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_2d725804-2b58-4529-b3a8-ded122e8fe7d" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019bfeff-82d5-7a4c-8385-489519e6b09f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bfeff-82d5-7a4c-8385-489519e6b09f_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019bfeff-82d5-7a4c-8385-489519e6b09f" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bfeff-82d5-7a4c-8385-489519e6b09f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bfeff-82d5-7c33-9511-39844f218df2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019bfeff-82d5-7a4c-8385-489519e6b09f" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bfeff-82d5-7c33-9511-39844f218df2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosABBSAMember_019bfeff-82d5-73de-9562-4afcbd11f6af" xlink:href="abvx-20251231.xsd#abvx_KreosABBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bfeff-82d5-7c33-9511-39844f218df2" xlink:to="loc_abvx_KreosABBSAMember_019bfeff-82d5-73de-9562-4afcbd11f6af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretMinimumReturnIndemnificationsMember_019bfeff-b745-7feb-9264-1834b1a0be71" xlink:href="abvx-20251231.xsd#abvx_KreosClaretMinimumReturnIndemnificationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bfeff-82d5-7c33-9511-39844f218df2" xlink:to="loc_abvx_KreosClaretMinimumReturnIndemnificationsMember_019bfeff-b745-7feb-9264-1834b1a0be71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosABCBSAMember_019bff0c-e052-7c62-95ab-804715793a0d" xlink:href="abvx-20251231.xsd#abvx_KreosABCBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bfeff-82d5-7c33-9511-39844f218df2" xlink:to="loc_abvx_KreosABCBSAMember_019bff0c-e052-7c62-95ab-804715793a0d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosCBSAMember_019c0047-c5e4-73fa-b949-2eaea9cdc692" xlink:href="abvx-20251231.xsd#abvx_KreosCBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bfeff-82d5-7c33-9511-39844f218df2" xlink:to="loc_abvx_KreosCBSAMember_019c0047-c5e4-73fa-b949-2eaea9cdc692" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsAxis_019bfeff-82d5-74c4-b079-e7d00424261e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_2d725804-2b58-4529-b3a8-ded122e8fe7d" xlink:to="loc_ifrs-full_UnobservableInputsAxis_019bfeff-82d5-74c4-b079-e7d00424261e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_019bfeff-82d5-74c4-b079-e7d00424261e_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_UnobservableInputsAxis_019bfeff-82d5-74c4-b079-e7d00424261e" xlink:to="loc_ifrs-full_UnobservableInputsDomain_019bfeff-82d5-74c4-b079-e7d00424261e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_019bfeff-82d5-7be8-9d48-6d4f77fd898a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_UnobservableInputsAxis_019bfeff-82d5-74c4-b079-e7d00424261e" xlink:to="loc_ifrs-full_UnobservableInputsDomain_019bfeff-82d5-7be8-9d48-6d4f77fd898a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_MarketRateMeasurementInputMember_019bfeff-82d5-7523-9de9-3cbb04860cd9" xlink:href="abvx-20251231.xsd#abvx_MarketRateMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bfeff-82d5-7be8-9d48-6d4f77fd898a" xlink:to="loc_abvx_MarketRateMeasurementInputMember_019bfeff-82d5-7523-9de9-3cbb04860cd9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SharePriceMeasurementInputMember_019bfeff-b745-7890-bc29-434581939a82" xlink:href="abvx-20251231.xsd#abvx_SharePriceMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bfeff-82d5-7be8-9d48-6d4f77fd898a" xlink:to="loc_abvx_SharePriceMeasurementInputMember_019bfeff-b745-7890-bc29-434581939a82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_HistoricalVolatilityForSharesMeasurementInputMember_019bfeff-b745-705d-8e84-9245cc16e966" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_HistoricalVolatilityForSharesMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bfeff-82d5-7be8-9d48-6d4f77fd898a" xlink:to="loc_ifrs-full_HistoricalVolatilityForSharesMeasurementInputMember_019bfeff-b745-705d-8e84-9245cc16e966" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RiskFreeInterestRateMeasurementInputMember_019bfeff-b745-77f5-80fc-36a6aded56d1" xlink:href="abvx-20251231.xsd#abvx_RiskFreeInterestRateMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bfeff-82d5-7be8-9d48-6d4f77fd898a" xlink:to="loc_abvx_RiskFreeInterestRateMeasurementInputMember_019bfeff-b745-77f5-80fc-36a6aded56d1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinalRedemptionScenarioProbabilityMeasurementInputMember_019bfeff-dc24-7392-8855-650ee886ba89" xlink:href="abvx-20251231.xsd#abvx_FinalRedemptionScenarioProbabilityMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bfeff-82d5-7be8-9d48-6d4f77fd898a" xlink:to="loc_abvx_FinalRedemptionScenarioProbabilityMeasurementInputMember_019bfeff-dc24-7392-8855-650ee886ba89" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DiscountRateMeasurementInputMember_019bfeff-dc24-7e70-830c-e64ff90ebba0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DiscountRateMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bfeff-82d5-7be8-9d48-6d4f77fd898a" xlink:to="loc_ifrs-full_DiscountRateMeasurementInputMember_019bfeff-dc24-7e70-830c-e64ff90ebba0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExpiryScenarioProbablityMeasurementInputMember_019bff0c-e052-72de-83bc-12d8873a63ba" xlink:href="abvx-20251231.xsd#abvx_ExpiryScenarioProbablityMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bfeff-82d5-7be8-9d48-6d4f77fd898a" xlink:to="loc_abvx_ExpiryScenarioProbablityMeasurementInputMember_019bff0c-e052-72de-83bc-12d8873a63ba" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_019bfeff-b745-7bad-b8eb-647b237b05e0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_2d725804-2b58-4529-b3a8-ded122e8fe7d" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_019bfeff-b745-7bad-b8eb-647b237b05e0" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_019bfeff-b745-7bad-b8eb-647b237b05e0_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_019bfeff-b745-7bad-b8eb-647b237b05e0" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_019bfeff-b745-7bad-b8eb-647b237b05e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_019bfeff-b745-7968-bfb8-80711a1ca811" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_019bfeff-b745-7bad-b8eb-647b237b05e0" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_019bfeff-b745-7968-bfb8-80711a1ca811" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BlackScholesModelMember_019bfeff-b745-7140-af40-8b22666e9e35" xlink:href="abvx-20251231.xsd#abvx_BlackScholesModelMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_019bfeff-b745-7968-bfb8-80711a1ca811" xlink:to="loc_abvx_BlackScholesModelMember_019bfeff-b745-7140-af40-8b22666e9e35" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_MonteCarloModel1Member_019bfeff-b745-7518-b21b-e7c80bc398f9" xlink:href="abvx-20251231.xsd#abvx_MonteCarloModel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_019bfeff-b745-7968-bfb8-80711a1ca811" xlink:to="loc_abvx_MonteCarloModel1Member_019bfeff-b745-7518-b21b-e7c80bc398f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis_019c56bf-5b1e-7528-936a-5999fe4b05aa" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_2d725804-2b58-4529-b3a8-ded122e8fe7d" xlink:to="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis_019c56bf-5b1e-7528-936a-5999fe4b05aa" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_019c56bf-5b1e-7528-936a-5999fe4b05aa_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis_019c56bf-5b1e-7528-936a-5999fe4b05aa" xlink:to="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_019c56bf-5b1e-7528-936a-5999fe4b05aa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_019c56bf-5b1e-7d91-a183-c5deb96b764e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis_019c56bf-5b1e-7528-936a-5999fe4b05aa" xlink:to="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_019c56bf-5b1e-7d91-a183-c5deb96b764e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos1ClaretBondLoansMember_019c56bf-5b1e-74da-a130-5cd79b88b1f6" xlink:href="abvx-20251231.xsd#abvx_Kreos1ClaretBondLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_019c56bf-5b1e-7d91-a183-c5deb96b764e" xlink:to="loc_abvx_Kreos1ClaretBondLoansMember_019c56bf-5b1e-74da-a130-5cd79b88b1f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsMaximumBorrowingCapacity_019bfefd-f0b7-790e-a120-38adabf2252a" xlink:href="abvx-20251231.xsd#abvx_BorrowingsMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_BorrowingsMaximumBorrowingCapacity_019bfefd-f0b7-790e-a120-38adabf2252a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RepaymentsOfBondLoans_019bfefe-b216-7ea3-9dd6-11e37f6e7e4d" xlink:href="abvx-20251231.xsd#abvx_RepaymentsOfBondLoans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_RepaymentsOfBondLoans_019bfefe-b216-7ea3-9dd6-11e37f6e7e4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsNumberOfTranches_019bfefd-f0b7-7398-bf8b-76b2676d1733" xlink:href="abvx-20251231.xsd#abvx_BorrowingsNumberOfTranches"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_BorrowingsNumberOfTranches_019bfefd-f0b7-7398-bf8b-76b2676d1733" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsMaximumBorrowingCapacityPerTranche_019bfefd-f0b7-7cd6-9dbb-576ae92b1802" xlink:href="abvx-20251231.xsd#abvx_BorrowingsMaximumBorrowingCapacityPerTranche"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_BorrowingsMaximumBorrowingCapacityPerTranche_019bfefd-f0b7-7cd6-9dbb-576ae92b1802" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProceedsFromBorrowingsClassifiedAsFinancingActivities_019bfefe-190c-72a2-a7a4-6da1222d670e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProceedsFromBorrowingsClassifiedAsFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_ProceedsFromBorrowingsClassifiedAsFinancingActivities_019bfefe-190c-72a2-a7a4-6da1222d670e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsFixedConversionPrice_019bfefe-190c-706b-b789-746eaa3a0546" xlink:href="abvx-20251231.xsd#abvx_BorrowingsFixedConversionPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_BorrowingsFixedConversionPrice_019bfefe-190c-706b-b789-746eaa3a0546" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsInterestRate_019bfefe-190c-75c6-b12c-59d045c6bc61" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_BorrowingsInterestRate_019bfefe-190c-75c6-b12c-59d045c6bc61" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsEarlyRepaymentDiscountRate_019bfefe-190c-7555-a078-76edd7de7f1f" xlink:href="abvx-20251231.xsd#abvx_BorrowingsEarlyRepaymentDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_BorrowingsEarlyRepaymentDiscountRate_019bfefe-190c-7555-a078-76edd7de7f1f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsExitFeePercentage_019bfefe-190c-7cf8-a383-946861fee68a" xlink:href="abvx-20251231.xsd#abvx_BorrowingsExitFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_BorrowingsExitFeePercentage_019bfefe-190c-7cf8-a383-946861fee68a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsDebtToMarketCapitalizationRatio_019bfefe-58cf-708d-b262-d0572d6c8076" xlink:href="abvx-20251231.xsd#abvx_BorrowingsDebtToMarketCapitalizationRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_BorrowingsDebtToMarketCapitalizationRatio_019bfefe-58cf-708d-b262-d0572d6c8076" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsPerformanceConditionsMinimumFinancing_019bfefe-58cf-73a3-8bd8-00fb5e5ed461" xlink:href="abvx-20251231.xsd#abvx_BorrowingsPerformanceConditionsMinimumFinancing"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_BorrowingsPerformanceConditionsMinimumFinancing_019bfefe-58cf-73a3-8bd8-00fb5e5ed461" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsAdjustmentToInterestRateBasis_019bfefe-58cf-734d-b3bb-6794ac3b9883" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsAdjustmentToInterestRateBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_BorrowingsAdjustmentToInterestRateBasis_019bfefe-58cf-734d-b3bb-6794ac3b9883" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsBasisInterestRate_019bfefe-58cf-711d-9b0b-60d2d4526d7a" xlink:href="abvx-20251231.xsd#abvx_BorrowingsBasisInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_BorrowingsBasisInterestRate_019bfefe-58cf-711d-9b0b-60d2d4526d7a" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherShareWarrantsSubscriptionPricePerShare_019bfefe-b216-7fca-9cf5-95e4d057b916" xlink:href="abvx-20251231.xsd#abvx_OtherShareWarrantsSubscriptionPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_OtherShareWarrantsSubscriptionPricePerShare_019bfefe-b216-7fca-9cf5-95e4d057b916" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfWarrantsGranted_019bfefe-b216-7334-9654-7b14b85d0646" xlink:href="abvx-20251231.xsd#abvx_NumberOfWarrantsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_NumberOfWarrantsGranted_019bfefe-b216-7334-9654-7b14b85d0646" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExercisePriceOtherEquityInstrumentsGranted_019bfefe-b216-77b8-8ee6-95a7f8b51e9d" xlink:href="abvx-20251231.xsd#abvx_ExercisePriceOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_ExercisePriceOtherEquityInstrumentsGranted_019bfefe-b216-77b8-8ee6-95a7f8b51e9d" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExercisePricePercentageOfPremiumOver15DayVWAPOtherEquityInstrumentsGranted_019bfefe-b216-731b-8247-c79689f4a7ee" xlink:href="abvx-20251231.xsd#abvx_ExercisePricePercentageOfPremiumOver15DayVWAPOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_ExercisePricePercentageOfPremiumOver15DayVWAPOtherEquityInstrumentsGranted_019bfefe-b216-731b-8247-c79689f4a7ee" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExercisePricePercentageOf15DayWVAPOtherEquityInstrumentsGranted_019bfefe-b216-7b22-9451-68ac6e300cdb" xlink:href="abvx-20251231.xsd#abvx_ExercisePricePercentageOf15DayWVAPOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_ExercisePricePercentageOf15DayWVAPOtherEquityInstrumentsGranted_019bfefe-b216-7b22-9451-68ac6e300cdb" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IssuanceOfOtherShareWarrants_019bfefe-b216-7a76-bc7d-57c7484c3888" xlink:href="abvx-20251231.xsd#abvx_IssuanceOfOtherShareWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_IssuanceOfOtherShareWarrants_019bfefe-b216-7a76-bc7d-57c7484c3888" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfInstrumentsGrantedOtherEquityInstrumentsPercentageExercisableImmediately_019bfefe-b216-7f5d-aba3-d1b1e0ef67b6" xlink:href="abvx-20251231.xsd#abvx_NumberOfInstrumentsGrantedOtherEquityInstrumentsPercentageExercisableImmediately"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_NumberOfInstrumentsGrantedOtherEquityInstrumentsPercentageExercisableImmediately_019bfefe-b216-7f5d-aba3-d1b1e0ef67b6" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfInstrumentsGrantedOtherEquityInstrumentsRemainingPercentageExercisable_019bfefe-b216-7319-b927-50206565ca44" xlink:href="abvx-20251231.xsd#abvx_NumberOfInstrumentsGrantedOtherEquityInstrumentsRemainingPercentageExercisable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_NumberOfInstrumentsGrantedOtherEquityInstrumentsRemainingPercentageExercisable_019bfefe-b216-7319-b927-50206565ca44" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherShareWarrantsExercisePeriod_019bfefe-b216-7970-8ef6-0426d1d6929c" xlink:href="abvx-20251231.xsd#abvx_OtherShareWarrantsExercisePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_OtherShareWarrantsExercisePeriod_019bfefe-b216-7970-8ef6-0426d1d6929c" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughConversionOfConvertibleInstruments_019bfefe-d819-7e34-9eca-c12f279daaa5" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughConversionOfConvertibleInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughConversionOfConvertibleInstruments_019bfefe-d819-7e34-9eca-c12f279daaa5" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughConversionOfConvertibleInstruments_019bfefe-d819-7ec0-a72a-1b4c9d30aba1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughConversionOfConvertibleInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughConversionOfConvertibleInstruments_019bfefe-d819-7ec0-a72a-1b4c9d30aba1" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfWarrantsRepurchased_019bfefe-d819-78dd-b858-386bfe8107a0" xlink:href="abvx-20251231.xsd#abvx_NumberOfWarrantsRepurchased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_NumberOfWarrantsRepurchased_019bfefe-d819-78dd-b858-386bfe8107a0" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants_019bfefe-d819-76b6-853c-da7f044c3269" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants_019bfefe-d819-76b6-853c-da7f044c3269" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughExerciseOfWarrantsEquity_019cfcce-9713-73cb-a6dc-5cecf1a7dceb" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughExerciseOfWarrantsEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughExerciseOfWarrantsEquity_019cfcce-9713-73cb-a6dc-5cecf1a7dceb" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AggregateFairValueOtherEquityInstrumentsOutstanding_019bfeff-00b5-7325-8631-ade5906ff8ce" xlink:href="abvx-20251231.xsd#abvx_AggregateFairValueOtherEquityInstrumentsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_AggregateFairValueOtherEquityInstrumentsOutstanding_019bfeff-00b5-7325-8631-ade5906ff8ce" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RepaymentsOfBorrowingsClassifiedAsFinancingActivities_019c56b3-373e-7d6b-9806-84dd9630a285" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RepaymentsOfBorrowingsClassifiedAsFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_RepaymentsOfBorrowingsClassifiedAsFinancingActivities_019c56b3-373e-7d6b-9806-84dd9630a285" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_Borrowings_019c56bb-c8ad-7a1d-aa49-105f5750d0fd" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Borrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_Borrowings_019c56bb-c8ad-7a1d-aa49-105f5750d0fd" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsDeposit_019c56b4-da50-7300-a5b4-9fe89fb33835" xlink:href="abvx-20251231.xsd#abvx_BorrowingsDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_BorrowingsDeposit_019c56b4-da50-7300-a5b4-9fe89fb33835" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsDiscountRate_019c56bd-58fc-7f8e-828e-1a4251c5a793" xlink:href="abvx-20251231.xsd#abvx_BorrowingsDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_BorrowingsDiscountRate_019c56bd-58fc-7f8e-828e-1a4251c5a793" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_InterestExpenseOnBorrowings_019c56ba-78b5-71cb-af61-30c8b159f573" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_InterestExpenseOnBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_InterestExpenseOnBorrowings_019c56ba-78b5-71cb-af61-30c8b159f573" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsExitFeeAmount_019c57ec-2964-7cc1-a9c1-aa3bdeac1ba4" xlink:href="abvx-20251231.xsd#abvx_BorrowingsExitFeeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_BorrowingsExitFeeAmount_019c57ec-2964-7cc1-a9c1-aa3bdeac1ba4" xlink:type="arc" order="33"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GainLossArisingFromDifferenceBetweenCarryingAmountOfFinancialLiabilityExtinguishedAndConsiderationPaid_019c56c6-6e6f-7865-b098-1eee8ae22e25" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GainLossArisingFromDifferenceBetweenCarryingAmountOfFinancialLiabilityExtinguishedAndConsiderationPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_GainLossArisingFromDifferenceBetweenCarryingAmountOfFinancialLiabilityExtinguishedAndConsiderationPaid_019c56c6-6e6f-7865-b098-1eee8ae22e25" xlink:type="arc" order="34"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NotionalAmount_019c56d5-139c-7bf5-a5fb-32d5ee832f4a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_NotionalAmount_019c56d5-139c-7bf5-a5fb-32d5ee832f4a" xlink:type="arc" order="35"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_FinancialLiabilitiesAtFairValue_019bfeff-82d5-7687-91e5-b85640ccec44" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FinancialLiabilitiesAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_FinancialLiabilitiesAtFairValue_019bfeff-82d5-7687-91e5-b85640ccec44" xlink:type="arc" order="36"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_SignificantUnobservableInputLiabilities_019bfeff-82d5-7e60-af27-9c7bb84a1892" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SignificantUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_SignificantUnobservableInputLiabilities_019bfeff-82d5-7e60-af27-9c7bb84a1892" xlink:type="arc" order="37"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConvertibleLoansNotes_019bfeff-82d5-79dd-84ce-297e6d15e1d9" xlink:href="abvx-20251231.xsd#abvx_ConvertibleLoansNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_ConvertibleLoansNotes_019bfeff-82d5-79dd-84ce-297e6d15e1d9" xlink:type="arc" order="38"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConvertibleLoansNotesCarryingAmountOfTheEquityComponent_019bfeff-82d5-7b04-ac27-3d08313b0bd6" xlink:href="abvx-20251231.xsd#abvx_ConvertibleLoansNotesCarryingAmountOfTheEquityComponent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_ConvertibleLoansNotesCarryingAmountOfTheEquityComponent_019bfeff-82d5-7b04-ac27-3d08313b0bd6" xlink:type="arc" order="39"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bfeff-82d5-72b5-83b6-cbd5d8a5b024" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bfeff-82d5-72b5-83b6-cbd5d8a5b024" xlink:type="arc" order="40"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bfeff-82d5-7fb2-9fd3-3b35ba90d069" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bfeff-82d5-7fb2-9fd3-3b35ba90d069" xlink:type="arc" order="41"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AmountOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bfeff-dc24-7094-8820-4c4406c53691" xlink:href="abvx-20251231.xsd#abvx_AmountOfReasonablyPossibleIncreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_AmountOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bfeff-dc24-7094-8820-4c4406c53691" xlink:type="arc" order="42"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputAssets_019bfeff-dc24-704e-856f-eebc0671514d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputAssets_019bfeff-dc24-704e-856f-eebc0671514d" xlink:type="arc" order="43"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExpiryScenarioPeriodOtherEquityInstrumentsGranted_019bff0c-e052-708d-a4c3-19905e9ff88e" xlink:href="abvx-20251231.xsd#abvx_ExpiryScenarioPeriodOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_abvx_ExpiryScenarioPeriodOtherEquityInstrumentsGranted_019bff0c-e052-708d-a4c3-19905e9ff88e" xlink:type="arc" order="44"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughChangesInFairValuesLiabilitiesArisingFromFinancingActivities_019c56bf-5b1e-73fb-baa0-823b1300875f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughChangesInFairValuesLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bfefd-f0b7-755e-8458-c5a0425f953a" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughChangesInFairValuesLiabilitiesArisingFromFinancingActivities_019c56bf-5b1e-73fb-baa0-823b1300875f" xlink:type="arc" order="45"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesDisclosureofthemaindataandassumptionsKreosClaretminimumreturnindemnificationsDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesDisclosureofthemaindataandassumptionsKreosClaretminimumreturnindemnificationsDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesDisclosureofthemaindataandassumptionsKreosClaretminimumreturnindemnificationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_9872e8ad-dc13-43ab-a0f3-9d170405ce0f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_36cd83a0-7931-48fc-b0df-94f3b271081f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_9872e8ad-dc13-43ab-a0f3-9d170405ce0f" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_36cd83a0-7931-48fc-b0df-94f3b271081f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfLiabilitiesAxis_a84674cd-1a26-4dd5-b547-078dee1358fa" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_36cd83a0-7931-48fc-b0df-94f3b271081f" xlink:to="loc_ifrs-full_ClassesOfLiabilitiesAxis_a84674cd-1a26-4dd5-b547-078dee1358fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfLiabilitiesDomain_a84674cd-1a26-4dd5-b547-078dee1358fa_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesAxis_a84674cd-1a26-4dd5-b547-078dee1358fa" xlink:to="loc_ifrs-full_ClassesOfLiabilitiesDomain_a84674cd-1a26-4dd5-b547-078dee1358fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfLiabilitiesDomain_06bcadf2-00bd-4f1d-9716-8b1820858b45" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesAxis_a84674cd-1a26-4dd5-b547-078dee1358fa" xlink:to="loc_ifrs-full_ClassesOfLiabilitiesDomain_06bcadf2-00bd-4f1d-9716-8b1820858b45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretMinimumReturnIndemnificationsMember_94e984e7-b7d7-43b3-b648-fec3925fc43e" xlink:href="abvx-20251231.xsd#abvx_KreosClaretMinimumReturnIndemnificationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesDomain_06bcadf2-00bd-4f1d-9716-8b1820858b45" xlink:to="loc_abvx_KreosClaretMinimumReturnIndemnificationsMember_94e984e7-b7d7-43b3-b648-fec3925fc43e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsAxis_768050a3-57f8-487a-b829-3f09a7798321" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_36cd83a0-7931-48fc-b0df-94f3b271081f" xlink:to="loc_ifrs-full_UnobservableInputsAxis_768050a3-57f8-487a-b829-3f09a7798321" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_768050a3-57f8-487a-b829-3f09a7798321_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_UnobservableInputsAxis_768050a3-57f8-487a-b829-3f09a7798321" xlink:to="loc_ifrs-full_UnobservableInputsDomain_768050a3-57f8-487a-b829-3f09a7798321_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_13497e69-3221-4bae-849d-162e23accfba" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_UnobservableInputsAxis_768050a3-57f8-487a-b829-3f09a7798321" xlink:to="loc_ifrs-full_UnobservableInputsDomain_13497e69-3221-4bae-849d-162e23accfba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinalRedemptionScenarioProbabilityMeasurementInputMember_68a89ecb-c5e5-408f-91ef-0c48f92e9f24" xlink:href="abvx-20251231.xsd#abvx_FinalRedemptionScenarioProbabilityMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_13497e69-3221-4bae-849d-162e23accfba" xlink:to="loc_abvx_FinalRedemptionScenarioProbabilityMeasurementInputMember_68a89ecb-c5e5-408f-91ef-0c48f92e9f24" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_MinimalReturnMeasurementInputMember_00eb163c-99bf-48c5-8ab6-4f7ff4e202b2" xlink:href="abvx-20251231.xsd#abvx_MinimalReturnMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_13497e69-3221-4bae-849d-162e23accfba" xlink:to="loc_abvx_MinimalReturnMeasurementInputMember_00eb163c-99bf-48c5-8ab6-4f7ff4e202b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DiscountRateMeasurementInputMember_d977269c-5c93-4964-b1d0-d54ee84527c0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DiscountRateMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_13497e69-3221-4bae-849d-162e23accfba" xlink:to="loc_ifrs-full_DiscountRateMeasurementInputMember_d977269c-5c93-4964-b1d0-d54ee84527c0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinalRedemptionProbabilityWeightedPresentValueOfShortfallPaymentMeasurementInputMember_65d80013-b519-4c4b-9df2-9bab15aa222a" xlink:href="abvx-20251231.xsd#abvx_FinalRedemptionProbabilityWeightedPresentValueOfShortfallPaymentMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_13497e69-3221-4bae-849d-162e23accfba" xlink:to="loc_abvx_FinalRedemptionProbabilityWeightedPresentValueOfShortfallPaymentMeasurementInputMember_65d80013-b519-4c4b-9df2-9bab15aa222a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TenderOfferProbabilityWeightedPresentValueOfShortfallPaymentMeasurementInputMember_916024b2-f762-4677-b25a-a0995c10ef93" xlink:href="abvx-20251231.xsd#abvx_TenderOfferProbabilityWeightedPresentValueOfShortfallPaymentMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_13497e69-3221-4bae-849d-162e23accfba" xlink:to="loc_abvx_TenderOfferProbabilityWeightedPresentValueOfShortfallPaymentMeasurementInputMember_916024b2-f762-4677-b25a-a0995c10ef93" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinalRedemptionProbabilityWeightedFairValueWithMRIMeasurementInputMember_f36618a9-1e2f-43c6-9250-d6c668797a3a" xlink:href="abvx-20251231.xsd#abvx_FinalRedemptionProbabilityWeightedFairValueWithMRIMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_13497e69-3221-4bae-849d-162e23accfba" xlink:to="loc_abvx_FinalRedemptionProbabilityWeightedFairValueWithMRIMeasurementInputMember_f36618a9-1e2f-43c6-9250-d6c668797a3a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinalRedemptionProbabilityWeightedFairValueWithoutMRIMeasurementInputMember_8af5ce17-404c-41a9-837f-6de6b0d11ffb" xlink:href="abvx-20251231.xsd#abvx_FinalRedemptionProbabilityWeightedFairValueWithoutMRIMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_13497e69-3221-4bae-849d-162e23accfba" xlink:to="loc_abvx_FinalRedemptionProbabilityWeightedFairValueWithoutMRIMeasurementInputMember_8af5ce17-404c-41a9-837f-6de6b0d11ffb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinalRedemptionFairValueOfMRIMeasurementInputMember_7265268a-6add-4bf4-aa1a-9745fb699b8c" xlink:href="abvx-20251231.xsd#abvx_FinalRedemptionFairValueOfMRIMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_13497e69-3221-4bae-849d-162e23accfba" xlink:to="loc_abvx_FinalRedemptionFairValueOfMRIMeasurementInputMember_7265268a-6add-4bf4-aa1a-9745fb699b8c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TenderOfferFairValueOfMRIMeasurementInputMember_c97f3eb8-8833-497e-84cd-8c302e4372ac" xlink:href="abvx-20251231.xsd#abvx_TenderOfferFairValueOfMRIMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_13497e69-3221-4bae-849d-162e23accfba" xlink:to="loc_abvx_TenderOfferFairValueOfMRIMeasurementInputMember_c97f3eb8-8833-497e-84cd-8c302e4372ac" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_b1590cdc-d247-4ac7-b801-bc3a84f5656a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_36cd83a0-7931-48fc-b0df-94f3b271081f" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_b1590cdc-d247-4ac7-b801-bc3a84f5656a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_b1590cdc-d247-4ac7-b801-bc3a84f5656a_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_b1590cdc-d247-4ac7-b801-bc3a84f5656a" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_b1590cdc-d247-4ac7-b801-bc3a84f5656a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_7b61290a-2065-40b2-a3b2-447e5ccd344d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_b1590cdc-d247-4ac7-b801-bc3a84f5656a" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_7b61290a-2065-40b2-a3b2-447e5ccd344d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AmortizedCostEIRMethodMember_70cbd0d6-8c2b-4de2-9475-3c8240d70e3a" xlink:href="abvx-20251231.xsd#abvx_AmortizedCostEIRMethodMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_7b61290a-2065-40b2-a3b2-447e5ccd344d" xlink:to="loc_abvx_AmortizedCostEIRMethodMember_70cbd0d6-8c2b-4de2-9475-3c8240d70e3a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesAxis_e182b80b-b796-4c25-96ea-19da86e25baa" xlink:href="abvx-20251231.xsd#abvx_TranchesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_36cd83a0-7931-48fc-b0df-94f3b271081f" xlink:to="loc_abvx_TranchesAxis_e182b80b-b796-4c25-96ea-19da86e25baa" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesDomain_e182b80b-b796-4c25-96ea-19da86e25baa_default" xlink:href="abvx-20251231.xsd#abvx_TranchesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_TranchesAxis_e182b80b-b796-4c25-96ea-19da86e25baa" xlink:to="loc_abvx_TranchesDomain_e182b80b-b796-4c25-96ea-19da86e25baa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TranchesDomain_9e1e2092-4488-4e98-a620-1a08d01656e9" xlink:href="abvx-20251231.xsd#abvx_TranchesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_TranchesAxis_e182b80b-b796-4c25-96ea-19da86e25baa" xlink:to="loc_abvx_TranchesDomain_9e1e2092-4488-4e98-a620-1a08d01656e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheBMember_1d4d516c-bdf6-4262-a8f2-8df550cb4c07" xlink:href="abvx-20251231.xsd#abvx_TrancheBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_9e1e2092-4488-4e98-a620-1a08d01656e9" xlink:to="loc_abvx_TrancheBMember_1d4d516c-bdf6-4262-a8f2-8df550cb4c07" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TrancheCMember_d26ff512-170d-4682-a733-23c6fbb3fa7e" xlink:href="abvx-20251231.xsd#abvx_TrancheCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_TranchesDomain_9e1e2092-4488-4e98-a620-1a08d01656e9" xlink:to="loc_abvx_TrancheCMember_d26ff512-170d-4682-a733-23c6fbb3fa7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_SignificantUnobservableInputLiabilities_7d715588-af4a-4813-bc29-c81392ee0579" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SignificantUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_9872e8ad-dc13-43ab-a0f3-9d170405ce0f" xlink:to="loc_ifrs-full_SignificantUnobservableInputLiabilities_7d715588-af4a-4813-bc29-c81392ee0579" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AggregateFairValueOtherEquityInstrumentsOutstanding_efc7bee9-461d-4579-8450-73a957fd4c73" xlink:href="abvx-20251231.xsd#abvx_AggregateFairValueOtherEquityInstrumentsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_9872e8ad-dc13-43ab-a0f3-9d170405ce0f" xlink:to="loc_abvx_AggregateFairValueOtherEquityInstrumentsOutstanding_efc7bee9-461d-4579-8450-73a957fd4c73" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesDisclosureofthemaindataandassumptionsKreosClaretBSADetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesDisclosureofthemaindataandassumptionsKreosClaretBSADetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesDisclosureofthemaindataandassumptionsKreosClaretBSADetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfWarrantsArrangementsLineItems_d7994492-1e50-4fc6-a2ab-b3d7fe738371" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfWarrantsArrangementsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfWarrantsArrangementsTable_10900a4b-72f0-4dcd-bef1-1eb16b6a3947" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfWarrantsArrangementsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsLineItems_d7994492-1e50-4fc6-a2ab-b3d7fe738371" xlink:to="loc_abvx_DisclosureOfWarrantsArrangementsTable_10900a4b-72f0-4dcd-bef1-1eb16b6a3947" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsAxis_3a452a7e-63be-45fc-b642-9950260545a1" xlink:href="abvx-20251231.xsd#abvx_WarrantsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsTable_10900a4b-72f0-4dcd-bef1-1eb16b6a3947" xlink:to="loc_abvx_WarrantsAxis_3a452a7e-63be-45fc-b642-9950260545a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsDomain_3a452a7e-63be-45fc-b642-9950260545a1_default" xlink:href="abvx-20251231.xsd#abvx_WarrantsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_WarrantsAxis_3a452a7e-63be-45fc-b642-9950260545a1" xlink:to="loc_abvx_WarrantsDomain_3a452a7e-63be-45fc-b642-9950260545a1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsDomain_1c2ea615-bac9-47b1-8434-1019915c82fc" xlink:href="abvx-20251231.xsd#abvx_WarrantsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_WarrantsAxis_3a452a7e-63be-45fc-b642-9950260545a1" xlink:to="loc_abvx_WarrantsDomain_1c2ea615-bac9-47b1-8434-1019915c82fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosABBSAMember_ceaea5e7-c61b-47d9-ae14-dc7208568f89" xlink:href="abvx-20251231.xsd#abvx_KreosABBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_WarrantsDomain_1c2ea615-bac9-47b1-8434-1019915c82fc" xlink:to="loc_abvx_KreosABBSAMember_ceaea5e7-c61b-47d9-ae14-dc7208568f89" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosCBSAMember_bff0f80f-1b07-45cd-b25c-326601e5f69d" xlink:href="abvx-20251231.xsd#abvx_KreosCBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_WarrantsDomain_1c2ea615-bac9-47b1-8434-1019915c82fc" xlink:to="loc_abvx_KreosCBSAMember_bff0f80f-1b07-45cd-b25c-326601e5f69d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfLiabilitiesAxis_b8db9b02-bb20-4132-8c72-1ef096aa02f8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsTable_10900a4b-72f0-4dcd-bef1-1eb16b6a3947" xlink:to="loc_ifrs-full_ClassesOfLiabilitiesAxis_b8db9b02-bb20-4132-8c72-1ef096aa02f8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfLiabilitiesDomain_b8db9b02-bb20-4132-8c72-1ef096aa02f8_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesAxis_b8db9b02-bb20-4132-8c72-1ef096aa02f8" xlink:to="loc_ifrs-full_ClassesOfLiabilitiesDomain_b8db9b02-bb20-4132-8c72-1ef096aa02f8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfLiabilitiesDomain_05b99197-9573-442b-9fe4-36ba04f9521f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesAxis_b8db9b02-bb20-4132-8c72-1ef096aa02f8" xlink:to="loc_ifrs-full_ClassesOfLiabilitiesDomain_05b99197-9573-442b-9fe4-36ba04f9521f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosABBSAMember_4b51b439-eee7-4bd9-a318-05419921d67b" xlink:href="abvx-20251231.xsd#abvx_KreosABBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesDomain_05b99197-9573-442b-9fe4-36ba04f9521f" xlink:to="loc_abvx_KreosABBSAMember_4b51b439-eee7-4bd9-a318-05419921d67b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosCBSAMember_6e097aea-66dc-455d-bda3-1cb2ee73ca38" xlink:href="abvx-20251231.xsd#abvx_KreosCBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfLiabilitiesDomain_05b99197-9573-442b-9fe4-36ba04f9521f" xlink:to="loc_abvx_KreosCBSAMember_6e097aea-66dc-455d-bda3-1cb2ee73ca38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_9b25b42f-6eca-4b28-bb28-f138c05e5663" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsTable_10900a4b-72f0-4dcd-bef1-1eb16b6a3947" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_9b25b42f-6eca-4b28-bb28-f138c05e5663" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_9b25b42f-6eca-4b28-bb28-f138c05e5663_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_9b25b42f-6eca-4b28-bb28-f138c05e5663" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_9b25b42f-6eca-4b28-bb28-f138c05e5663_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_af52823c-9cf6-41b3-932e-3af301f83a22" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_9b25b42f-6eca-4b28-bb28-f138c05e5663" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_af52823c-9cf6-41b3-932e-3af301f83a22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OptionPricingModelMember_8ba5ca94-62fd-4787-ae19-a8980c39b5ca" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OptionPricingModelMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_af52823c-9cf6-41b3-932e-3af301f83a22" xlink:to="loc_ifrs-full_OptionPricingModelMember_8ba5ca94-62fd-4787-ae19-a8980c39b5ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsAxis_e1b99aac-5813-4b22-bc78-03c11c715f48" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsTable_10900a4b-72f0-4dcd-bef1-1eb16b6a3947" xlink:to="loc_ifrs-full_UnobservableInputsAxis_e1b99aac-5813-4b22-bc78-03c11c715f48" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_e1b99aac-5813-4b22-bc78-03c11c715f48_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_UnobservableInputsAxis_e1b99aac-5813-4b22-bc78-03c11c715f48" xlink:to="loc_ifrs-full_UnobservableInputsDomain_e1b99aac-5813-4b22-bc78-03c11c715f48_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_1ea3f684-57da-4869-b3e6-ff6b1f8ca68f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_UnobservableInputsAxis_e1b99aac-5813-4b22-bc78-03c11c715f48" xlink:to="loc_ifrs-full_UnobservableInputsDomain_1ea3f684-57da-4869-b3e6-ff6b1f8ca68f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExercisePricePerShareMeasurementInputMember_c83ed6e0-32cf-435a-b205-89e9d907a641" xlink:href="abvx-20251231.xsd#abvx_ExercisePricePerShareMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_1ea3f684-57da-4869-b3e6-ff6b1f8ca68f" xlink:to="loc_abvx_ExercisePricePerShareMeasurementInputMember_c83ed6e0-32cf-435a-b205-89e9d907a641" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SharePriceMeasurementInputMember_e7a442ae-d47e-4d92-b400-087cd5f747e3" xlink:href="abvx-20251231.xsd#abvx_SharePriceMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_1ea3f684-57da-4869-b3e6-ff6b1f8ca68f" xlink:to="loc_abvx_SharePriceMeasurementInputMember_e7a442ae-d47e-4d92-b400-087cd5f747e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExpiryScenarioProbablityMeasurementInputMember_bff38aa4-36ac-41d3-9bd6-f725b81a0941" xlink:href="abvx-20251231.xsd#abvx_ExpiryScenarioProbablityMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_1ea3f684-57da-4869-b3e6-ff6b1f8ca68f" xlink:to="loc_abvx_ExpiryScenarioProbablityMeasurementInputMember_bff38aa4-36ac-41d3-9bd6-f725b81a0941" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DrawdownProbablityMeasurementInputMember_33e6a508-5ca8-41f7-ad6c-dcf230cf1d22" xlink:href="abvx-20251231.xsd#abvx_DrawdownProbablityMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_1ea3f684-57da-4869-b3e6-ff6b1f8ca68f" xlink:to="loc_abvx_DrawdownProbablityMeasurementInputMember_33e6a508-5ca8-41f7-ad6c-dcf230cf1d22" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VolatilityForSharesMeasurementInputExpiryMember_c980c27c-a675-47dc-b0e4-3024763d6706" xlink:href="abvx-20251231.xsd#abvx_VolatilityForSharesMeasurementInputExpiryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_1ea3f684-57da-4869-b3e6-ff6b1f8ca68f" xlink:to="loc_abvx_VolatilityForSharesMeasurementInputExpiryMember_c980c27c-a675-47dc-b0e4-3024763d6706" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VolatilityForSharesMeasurementInputTenderOfferMember_43c9b57c-bc26-4b05-98df-a9e374ca5d8b" xlink:href="abvx-20251231.xsd#abvx_VolatilityForSharesMeasurementInputTenderOfferMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_1ea3f684-57da-4869-b3e6-ff6b1f8ca68f" xlink:to="loc_abvx_VolatilityForSharesMeasurementInputTenderOfferMember_43c9b57c-bc26-4b05-98df-a9e374ca5d8b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExpectedDividendMeasurementInputMember_d24025c8-ede3-4660-b0ec-a39ff6ea81cb" xlink:href="abvx-20251231.xsd#abvx_ExpectedDividendMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_1ea3f684-57da-4869-b3e6-ff6b1f8ca68f" xlink:to="loc_abvx_ExpectedDividendMeasurementInputMember_d24025c8-ede3-4660-b0ec-a39ff6ea81cb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RiskFreeInterestRateMeasurementInputMember_72b958c6-3b1d-400e-b260-cbfd799b326a" xlink:href="abvx-20251231.xsd#abvx_RiskFreeInterestRateMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_1ea3f684-57da-4869-b3e6-ff6b1f8ca68f" xlink:to="loc_abvx_RiskFreeInterestRateMeasurementInputMember_72b958c6-3b1d-400e-b260-cbfd799b326a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RiskFreeInterestRateMeasurementInputExpiryMember_ae5061f2-98a8-470e-a975-c236f86a8c7a" xlink:href="abvx-20251231.xsd#abvx_RiskFreeInterestRateMeasurementInputExpiryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_1ea3f684-57da-4869-b3e6-ff6b1f8ca68f" xlink:to="loc_abvx_RiskFreeInterestRateMeasurementInputExpiryMember_ae5061f2-98a8-470e-a975-c236f86a8c7a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RiskFreeInterestRateMeasurementInputTenderOfferMember_e490440b-84f5-406f-8654-0847580de6cc" xlink:href="abvx-20251231.xsd#abvx_RiskFreeInterestRateMeasurementInputTenderOfferMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_1ea3f684-57da-4869-b3e6-ff6b1f8ca68f" xlink:to="loc_abvx_RiskFreeInterestRateMeasurementInputTenderOfferMember_e490440b-84f5-406f-8654-0847580de6cc" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfProbabilityWeightedScenarios_4946f6e1-9293-4db8-9933-1415b1d8f7ec" xlink:href="abvx-20251231.xsd#abvx_NumberOfProbabilityWeightedScenarios"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsLineItems_d7994492-1e50-4fc6-a2ab-b3d7fe738371" xlink:to="loc_abvx_NumberOfProbabilityWeightedScenarios_4946f6e1-9293-4db8-9933-1415b1d8f7ec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExpiryScenarioPeriodOtherEquityInstrumentsGranted_9cf42215-b004-4674-aa40-a31f52568d2a" xlink:href="abvx-20251231.xsd#abvx_ExpiryScenarioPeriodOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsLineItems_d7994492-1e50-4fc6-a2ab-b3d7fe738371" xlink:to="loc_abvx_ExpiryScenarioPeriodOtherEquityInstrumentsGranted_9cf42215-b004-4674-aa40-a31f52568d2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfWarrantsOutstanding_9369da01-f1f2-4660-95b9-9617be73e253" xlink:href="abvx-20251231.xsd#abvx_NumberOfWarrantsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsLineItems_d7994492-1e50-4fc6-a2ab-b3d7fe738371" xlink:to="loc_abvx_NumberOfWarrantsOutstanding_9369da01-f1f2-4660-95b9-9617be73e253" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfWarrantsOutstandingSubjectToNonMarketPerformanceCondition_f2719dee-12dc-4188-b8de-9093f8b9bc30" xlink:href="abvx-20251231.xsd#abvx_NumberOfWarrantsOutstandingSubjectToNonMarketPerformanceCondition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsLineItems_d7994492-1e50-4fc6-a2ab-b3d7fe738371" xlink:to="loc_abvx_NumberOfWarrantsOutstandingSubjectToNonMarketPerformanceCondition_f2719dee-12dc-4188-b8de-9093f8b9bc30" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_SignificantUnobservableInputLiabilities_0548aa26-b075-4d10-af03-ddb2486b8ab6" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SignificantUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsLineItems_d7994492-1e50-4fc6-a2ab-b3d7fe738371" xlink:to="loc_ifrs-full_SignificantUnobservableInputLiabilities_0548aa26-b075-4d10-af03-ddb2486b8ab6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AggregateFairValueOtherEquityInstrumentsOutstanding_9d9e1fa2-1111-4bb8-9ea7-f0efd382e810" xlink:href="abvx-20251231.xsd#abvx_AggregateFairValueOtherEquityInstrumentsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsLineItems_d7994492-1e50-4fc6-a2ab-b3d7fe738371" xlink:to="loc_abvx_AggregateFairValueOtherEquityInstrumentsOutstanding_9d9e1fa2-1111-4bb8-9ea7-f0efd382e810" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesHeightsconvertiblenotesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesHeightsconvertiblenotesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesHeightsconvertiblenotesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_b068f566-e3c9-4f43-b0cd-3ff8579756cd" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_b068f566-e3c9-4f43-b0cd-3ff8579756cd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_019bff12-946a-7a51-bd9a-32e2f3205c7f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_b068f566-e3c9-4f43-b0cd-3ff8579756cd" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_019bff12-946a-7a51-bd9a-32e2f3205c7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019bff12-946a-7a51-bd9a-32e2f3205c7f_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019bff12-946a-7a51-bd9a-32e2f3205c7f" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019bff12-946a-7a51-bd9a-32e2f3205c7f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019bff12-946a-72c0-859d-d805b393d44a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019bff12-946a-7a51-bd9a-32e2f3205c7f" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019bff12-946a-72c0-859d-d805b393d44a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_HeightsConvertibleNotesMember_019bff12-946a-7472-a528-1e5927176811" xlink:href="abvx-20251231.xsd#abvx_HeightsConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bff12-946a-72c0-859d-d805b393d44a" xlink:to="loc_abvx_HeightsConvertibleNotesMember_019bff12-946a-7472-a528-1e5927176811" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_HeightsConvertibleNotesTrancheAMember_019bff12-946a-779e-bf7c-43680d555e8c" xlink:href="abvx-20251231.xsd#abvx_HeightsConvertibleNotesTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bff12-946a-72c0-859d-d805b393d44a" xlink:to="loc_abvx_HeightsConvertibleNotesTrancheAMember_019bff12-946a-779e-bf7c-43680d555e8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_HeightsConvertibleNotesTrancheBMember_019bff12-946a-7c20-824a-7644194ca7d3" xlink:href="abvx-20251231.xsd#abvx_HeightsConvertibleNotesTrancheBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bff12-946a-72c0-859d-d805b393d44a" xlink:to="loc_abvx_HeightsConvertibleNotesTrancheBMember_019bff12-946a-7c20-824a-7644194ca7d3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OCEANEMember_019bff13-18dc-7fa8-b908-2ce651b29da5" xlink:href="abvx-20251231.xsd#abvx_OCEANEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019bff12-946a-72c0-859d-d805b393d44a" xlink:to="loc_abvx_OCEANEMember_019bff13-18dc-7fa8-b908-2ce651b29da5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019bff12-946a-74cc-8a70-bd34e286ed55" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_b068f566-e3c9-4f43-b0cd-3ff8579756cd" xlink:to="loc_srt_RangeAxis_019bff12-946a-74cc-8a70-bd34e286ed55" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019bff12-946a-74cc-8a70-bd34e286ed55_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019bff12-946a-74cc-8a70-bd34e286ed55" xlink:to="loc_srt_RangeMember_019bff12-946a-74cc-8a70-bd34e286ed55_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019bff12-946a-71b0-8b53-e3a0cbd35648" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019bff12-946a-74cc-8a70-bd34e286ed55" xlink:to="loc_srt_RangeMember_019bff12-946a-71b0-8b53-e3a0cbd35648" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019bff12-946a-7500-a636-2f0ee1fd3944" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019bff12-946a-71b0-8b53-e3a0cbd35648" xlink:to="loc_srt_MinimumMember_019bff12-946a-7500-a636-2f0ee1fd3944" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019bff12-ec92-7c6e-8239-d37362a7659c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019bff12-946a-71b0-8b53-e3a0cbd35648" xlink:to="loc_srt_MaximumMember_019bff12-ec92-7c6e-8239-d37362a7659c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsAxis_019bff13-a23c-71b7-a9c0-541434254536" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_b068f566-e3c9-4f43-b0cd-3ff8579756cd" xlink:to="loc_ifrs-full_UnobservableInputsAxis_019bff13-a23c-71b7-a9c0-541434254536" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_019bff13-a23c-71b7-a9c0-541434254536_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_UnobservableInputsAxis_019bff13-a23c-71b7-a9c0-541434254536" xlink:to="loc_ifrs-full_UnobservableInputsDomain_019bff13-a23c-71b7-a9c0-541434254536_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_019bff13-a23c-7f06-b1ba-b956d500f3d7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_UnobservableInputsAxis_019bff13-a23c-71b7-a9c0-541434254536" xlink:to="loc_ifrs-full_UnobservableInputsDomain_019bff13-a23c-7f06-b1ba-b956d500f3d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_HistoricalVolatilityForSharesMeasurementInputMember_019bff13-a23c-7aaf-8965-46974d5e78f1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_HistoricalVolatilityForSharesMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bff13-a23c-7f06-b1ba-b956d500f3d7" xlink:to="loc_ifrs-full_HistoricalVolatilityForSharesMeasurementInputMember_019bff13-a23c-7aaf-8965-46974d5e78f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SharePriceMeasurementInputMember_019bff13-a23c-7480-8cdb-a47093bbe6e3" xlink:href="abvx-20251231.xsd#abvx_SharePriceMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bff13-a23c-7f06-b1ba-b956d500f3d7" xlink:to="loc_abvx_SharePriceMeasurementInputMember_019bff13-a23c-7480-8cdb-a47093bbe6e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RiskFreeInterestRateMeasurementInputMember_019bff13-a23c-710d-b8d9-ecfcbe68b08c" xlink:href="abvx-20251231.xsd#abvx_RiskFreeInterestRateMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bff13-a23c-7f06-b1ba-b956d500f3d7" xlink:to="loc_abvx_RiskFreeInterestRateMeasurementInputMember_019bff13-a23c-710d-b8d9-ecfcbe68b08c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VoluntaryConversionScenarioProbabilityMeasurementInputMember_019bff13-a23c-7c66-8400-debadf55571b" xlink:href="abvx-20251231.xsd#abvx_VoluntaryConversionScenarioProbabilityMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bff13-a23c-7f06-b1ba-b956d500f3d7" xlink:to="loc_abvx_VoluntaryConversionScenarioProbabilityMeasurementInputMember_019bff13-a23c-7c66-8400-debadf55571b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019bff13-a23c-7b01-9cac-3b84fd31dbef" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_b068f566-e3c9-4f43-b0cd-3ff8579756cd" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019bff13-a23c-7b01-9cac-3b84fd31dbef" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bff13-a23c-7b01-9cac-3b84fd31dbef_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019bff13-a23c-7b01-9cac-3b84fd31dbef" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bff13-a23c-7b01-9cac-3b84fd31dbef_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bff13-a23c-7887-8253-60037e437a8f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019bff13-a23c-7b01-9cac-3b84fd31dbef" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bff13-a23c-7887-8253-60037e437a8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_HeightsConvertibleNotesTrancheAMember_019bff13-a23c-7a80-b4b9-b278b97ac4ac" xlink:href="abvx-20251231.xsd#abvx_HeightsConvertibleNotesTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bff13-a23c-7887-8253-60037e437a8f" xlink:to="loc_abvx_HeightsConvertibleNotesTrancheAMember_019bff13-a23c-7a80-b4b9-b278b97ac4ac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsMaximumBorrowingCapacity_019bff12-946a-7a65-a938-28ef01967da8" xlink:href="abvx-20251231.xsd#abvx_BorrowingsMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_BorrowingsMaximumBorrowingCapacity_019bff12-946a-7a65-a938-28ef01967da8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsNumberOfTranches_019bff12-946a-7458-a4d3-4c1302c63185" xlink:href="abvx-20251231.xsd#abvx_BorrowingsNumberOfTranches"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_BorrowingsNumberOfTranches_019bff12-946a-7458-a4d3-4c1302c63185" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NetProceedsFromConvertibleLoansNotes_019bff12-946a-7c12-a2a1-368622ea9a9e" xlink:href="abvx-20251231.xsd#abvx_NetProceedsFromConvertibleLoansNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_NetProceedsFromConvertibleLoansNotes_019bff12-946a-7c12-a2a1-368622ea9a9e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfConvertibleNotesIssued_019bff12-946a-7457-8a27-5bbb0f6e8a3a" xlink:href="abvx-20251231.xsd#abvx_NumberOfConvertibleNotesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_NumberOfConvertibleNotesIssued_019bff12-946a-7457-8a27-5bbb0f6e8a3a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConvertibleLoansNotesNominalValue_019bff12-946a-7ceb-9448-a605232adf11" xlink:href="abvx-20251231.xsd#abvx_ConvertibleLoansNotesNominalValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_ConvertibleLoansNotesNominalValue_019bff12-946a-7ceb-9448-a605232adf11" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsFixedConversionPrice_019bff12-946a-786b-9995-408d0936a74d" xlink:href="abvx-20251231.xsd#abvx_BorrowingsFixedConversionPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_BorrowingsFixedConversionPrice_019bff12-946a-786b-9995-408d0936a74d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExercisePricePercentageOfPremiumOver15DayVWAPOtherEquityInstrumentsGranted_019bff12-946a-7b13-a6fc-04560f7c1f9a" xlink:href="abvx-20251231.xsd#abvx_ExercisePricePercentageOfPremiumOver15DayVWAPOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_ExercisePricePercentageOfPremiumOver15DayVWAPOtherEquityInstrumentsGranted_019bff12-946a-7b13-a6fc-04560f7c1f9a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NotionalAmount_019bff12-946a-7bf8-88b6-1b4ab6e7bfb6" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_ifrs-full_NotionalAmount_019bff12-946a-7bf8-88b6-1b4ab6e7bfb6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExercisePricePercentageOf15DayWVAPOtherEquityInstrumentsGranted_019bff12-946a-707b-bfcf-192831e0d9c1" xlink:href="abvx-20251231.xsd#abvx_ExercisePricePercentageOf15DayWVAPOtherEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_ExercisePricePercentageOf15DayWVAPOtherEquityInstrumentsGranted_019bff12-946a-707b-bfcf-192831e0d9c1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConvertibleLoansNotesPeriod_019bff12-946a-7550-a7c6-c121120a3ca5" xlink:href="abvx-20251231.xsd#abvx_ConvertibleLoansNotesPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_ConvertibleLoansNotesPeriod_019bff12-946a-7550-a7c6-c121120a3ca5" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConvertibleLoansNotesNumberOfSeparateClosings_019bff12-946a-719d-9b3d-7799e5eba37c" xlink:href="abvx-20251231.xsd#abvx_ConvertibleLoansNotesNumberOfSeparateClosings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_ConvertibleLoansNotesNumberOfSeparateClosings_019bff12-946a-719d-9b3d-7799e5eba37c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsInterestRate_019bff12-c4b9-7a05-b178-450221629cd9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_ifrs-full_BorrowingsInterestRate_019bff12-c4b9-7a05-b178-450221629cd9" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsNumberOfQuarterlyInstallments_019bff12-c4b9-7528-8ce5-0e50e2edd844" xlink:href="abvx-20251231.xsd#abvx_BorrowingsNumberOfQuarterlyInstallments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_BorrowingsNumberOfQuarterlyInstallments_019bff12-c4b9-7528-8ce5-0e50e2edd844" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsMaturityDeferralPeriod_019bff12-c4b9-72f9-aa91-ea09f34c8860" xlink:href="abvx-20251231.xsd#abvx_BorrowingsMaturityDeferralPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_BorrowingsMaturityDeferralPeriod_019bff12-c4b9-72f9-aa91-ea09f34c8860" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsPercentageOfMarketPrice_019bff12-c4b9-7ac1-b548-51b2f25ff480" xlink:href="abvx-20251231.xsd#abvx_BorrowingsPercentageOfMarketPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_BorrowingsPercentageOfMarketPrice_019bff12-c4b9-7ac1-b548-51b2f25ff480" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsMarketPriceNumberOfDaysWithLowestDailyVWAP_019bff12-c4b9-7d89-8118-7438cd5e8bf9" xlink:href="abvx-20251231.xsd#abvx_BorrowingsMarketPriceNumberOfDaysWithLowestDailyVWAP"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_BorrowingsMarketPriceNumberOfDaysWithLowestDailyVWAP_019bff12-c4b9-7d89-8118-7438cd5e8bf9" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsMarketPriceNumberOfTradingDays_019bff12-c4b9-76da-8d4f-7c5d6430c47b" xlink:href="abvx-20251231.xsd#abvx_BorrowingsMarketPriceNumberOfTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_BorrowingsMarketPriceNumberOfTradingDays_019bff12-c4b9-76da-8d4f-7c5d6430c47b" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IssuancePricePercentageOfDiscountTo15DayWVAP_019bff12-c4b9-7caf-b8e4-27b3b0c66c51" xlink:href="abvx-20251231.xsd#abvx_IssuancePricePercentageOfDiscountTo15DayWVAP"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_IssuancePricePercentageOfDiscountTo15DayWVAP_019bff12-c4b9-7caf-b8e4-27b3b0c66c51" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EquityIssuanceSubscriptionPricePerShare_019bff12-c4b9-797e-a06f-eb5c2e59cad1" xlink:href="abvx-20251231.xsd#abvx_EquityIssuanceSubscriptionPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_EquityIssuanceSubscriptionPricePerShare_019bff12-c4b9-797e-a06f-eb5c2e59cad1" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConvertibleLoansNotesSettlementInSharesPercentageOfFairMarketValue_019bff12-ec92-7d04-aace-5bb9c13dbc50" xlink:href="abvx-20251231.xsd#abvx_ConvertibleLoansNotesSettlementInSharesPercentageOfFairMarketValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_ConvertibleLoansNotesSettlementInSharesPercentageOfFairMarketValue_019bff12-ec92-7d04-aace-5bb9c13dbc50" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EquityIssuanceCashCarveOut_019bff12-ec92-71c0-9fd1-c08682ad0bb5" xlink:href="abvx-20251231.xsd#abvx_EquityIssuanceCashCarveOut"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_EquityIssuanceCashCarveOut_019bff12-ec92-71c0-9fd1-c08682ad0bb5" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConvertibleLoansNotesEarlyRedemptionAmountPercentageOfOutstandongPrincipal_019bff13-18dc-78bf-8644-4b9125257829" xlink:href="abvx-20251231.xsd#abvx_ConvertibleLoansNotesEarlyRedemptionAmountPercentageOfOutstandongPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_ConvertibleLoansNotesEarlyRedemptionAmountPercentageOfOutstandongPrincipal_019bff13-18dc-78bf-8644-4b9125257829" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RepaymentsOfConvertibleLoansNotes_019bff13-18dc-7a39-aa91-8443d6d056aa" xlink:href="abvx-20251231.xsd#abvx_RepaymentsOfConvertibleLoansNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_RepaymentsOfConvertibleLoansNotes_019bff13-18dc-7a39-aa91-8443d6d056aa" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfConvertibleNotesConverted_019bff13-3e5b-7e10-b6a3-94c78f8a82ea" xlink:href="abvx-20251231.xsd#abvx_NumberOfConvertibleNotesConverted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_NumberOfConvertibleNotesConverted_019bff13-3e5b-7e10-b6a3-94c78f8a82ea" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseInNumberOfOrdinarySharesIssued_019bff13-3e5b-73e8-8a05-e983be0b2719" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseInNumberOfOrdinarySharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_ifrs-full_IncreaseDecreaseInNumberOfOrdinarySharesIssued_019bff13-3e5b-73e8-8a05-e983be0b2719" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_GainsArisingFromRecognitionOfFinancialLiabilities_019bff13-6356-79b4-9788-8c6469a8a18f" xlink:href="abvx-20251231.xsd#abvx_GainsArisingFromRecognitionOfFinancialLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_GainsArisingFromRecognitionOfFinancialLiabilities_019bff13-6356-79b4-9788-8c6469a8a18f" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_UnrecognitionDayOneGainOfFinancialLiabilities_019bff13-6356-7aa1-a865-65ca279d5cbf" xlink:href="abvx-20251231.xsd#abvx_UnrecognitionDayOneGainOfFinancialLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_UnrecognitionDayOneGainOfFinancialLiabilities_019bff13-6356-7aa1-a865-65ca279d5cbf" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfProbabilityWeightedScenarios_019cfba1-980d-7a8e-8fd6-98b0a11a56bc" xlink:href="abvx-20251231.xsd#abvx_NumberOfProbabilityWeightedScenarios"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_NumberOfProbabilityWeightedScenarios_019cfba1-980d-7a8e-8fd6-98b0a11a56bc" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bff13-a23c-7f3f-a0da-d75585e988f2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bff13-a23c-7f3f-a0da-d75585e988f2" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AmountOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bff13-a23c-7bf0-b00a-532cfc13e21a" xlink:href="abvx-20251231.xsd#abvx_AmountOfReasonablyPossibleIncreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_AmountOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bff13-a23c-7bf0-b00a-532cfc13e21a" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputAssets_019bff13-a23c-7b5a-802c-64b3e29cd8cb" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputAssets_019bff13-a23c-7b5a-802c-64b3e29cd8cb" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughConversionOfConvertibleInstruments_019bff13-a23c-7d93-9021-98c761240786" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughConversionOfConvertibleInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughConversionOfConvertibleInstruments_019bff13-a23c-7d93-9021-98c761240786" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConvertibleLoansNotesConversionOptionMaximumPeriodPriorToMaturityDate_019c0044-9e8d-7861-a998-2c6f72f53d40" xlink:href="abvx-20251231.xsd#abvx_ConvertibleLoansNotesConversionOptionMaximumPeriodPriorToMaturityDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_ConvertibleLoansNotesConversionOptionMaximumPeriodPriorToMaturityDate_019c0044-9e8d-7861-a998-2c6f72f53d40" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_LossesOnFinancialLiabilitiesAssetsAtFairValueThroughProfitOrLoss_019cf6c5-e6dc-7754-b236-f928272ffd2e" xlink:href="abvx-20251231.xsd#abvx_LossesOnFinancialLiabilitiesAssetsAtFairValueThroughProfitOrLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bff12-946a-7f72-9612-caf5436cd585" xlink:to="loc_abvx_LossesOnFinancialLiabilitiesAssetsAtFairValueThroughProfitOrLoss_019cf6c5-e6dc-7754-b236-f928272ffd2e" xlink:type="arc" order="33"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesDisclosureofthemaindataandassumptionsHeightsconvertibleloannotesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesDisclosureofthemaindataandassumptionsHeightsconvertibleloannotesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesDisclosureofthemaindataandassumptionsHeightsconvertibleloannotesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfFinancialLiabilitiesLineItems_d337f439-0521-46ad-80b2-95d6ff073461" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfFinancialLiabilitiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfFinancialLiabilitiesTable_24ccb8fc-d0dc-4297-bc7e-6503ac2e3749" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfFinancialLiabilitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfFinancialLiabilitiesLineItems_d337f439-0521-46ad-80b2-95d6ff073461" xlink:to="loc_ifrs-full_DisclosureOfFinancialLiabilitiesTable_24ccb8fc-d0dc-4297-bc7e-6503ac2e3749" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_4bbdda24-5dae-4f0d-a518-1770da543fca" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfFinancialLiabilitiesTable_24ccb8fc-d0dc-4297-bc7e-6503ac2e3749" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_4bbdda24-5dae-4f0d-a518-1770da543fca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_4bbdda24-5dae-4f0d-a518-1770da543fca_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_4bbdda24-5dae-4f0d-a518-1770da543fca" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_4bbdda24-5dae-4f0d-a518-1770da543fca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_ba61a51c-f384-4ed5-bdfe-c4d01dde5ff4" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_4bbdda24-5dae-4f0d-a518-1770da543fca" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_ba61a51c-f384-4ed5-bdfe-c4d01dde5ff4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_HeightsConvertibleNotesTrancheAMember_7b351cf3-5294-48c4-bc8a-9699e27a5426" xlink:href="abvx-20251231.xsd#abvx_HeightsConvertibleNotesTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_ba61a51c-f384-4ed5-bdfe-c4d01dde5ff4" xlink:to="loc_abvx_HeightsConvertibleNotesTrancheAMember_7b351cf3-5294-48c4-bc8a-9699e27a5426" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsAxis_e3b939c6-993d-45c3-b1a4-b6d3c9a36309" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfFinancialLiabilitiesTable_24ccb8fc-d0dc-4297-bc7e-6503ac2e3749" xlink:to="loc_ifrs-full_UnobservableInputsAxis_e3b939c6-993d-45c3-b1a4-b6d3c9a36309" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_e3b939c6-993d-45c3-b1a4-b6d3c9a36309_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_UnobservableInputsAxis_e3b939c6-993d-45c3-b1a4-b6d3c9a36309" xlink:to="loc_ifrs-full_UnobservableInputsDomain_e3b939c6-993d-45c3-b1a4-b6d3c9a36309_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_697203e3-7f0c-40ea-8d83-109b440d3879" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_UnobservableInputsAxis_e3b939c6-993d-45c3-b1a4-b6d3c9a36309" xlink:to="loc_ifrs-full_UnobservableInputsDomain_697203e3-7f0c-40ea-8d83-109b440d3879" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_InterestRateMeasurementInputMember_23790f53-4d92-4693-9490-f89248714796" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_InterestRateMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_697203e3-7f0c-40ea-8d83-109b440d3879" xlink:to="loc_ifrs-full_InterestRateMeasurementInputMember_23790f53-4d92-4693-9490-f89248714796" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConversionPricePerShareMeasurementInputMember_db23499f-198e-4408-b2e9-dd0f560116df" xlink:href="abvx-20251231.xsd#abvx_ConversionPricePerShareMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_697203e3-7f0c-40ea-8d83-109b440d3879" xlink:to="loc_abvx_ConversionPricePerShareMeasurementInputMember_db23499f-198e-4408-b2e9-dd0f560116df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SharePriceMeasurementInputMember_299bee0c-563f-4ba9-81a8-08ce4ec3f828" xlink:href="abvx-20251231.xsd#abvx_SharePriceMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_697203e3-7f0c-40ea-8d83-109b440d3879" xlink:to="loc_abvx_SharePriceMeasurementInputMember_299bee0c-563f-4ba9-81a8-08ce4ec3f828" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_VoluntaryConversionScenarioProbabilityMeasurementInputMember_8e580454-3d5a-40b0-9305-3f14274a64ab" xlink:href="abvx-20251231.xsd#abvx_VoluntaryConversionScenarioProbabilityMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_697203e3-7f0c-40ea-8d83-109b440d3879" xlink:to="loc_abvx_VoluntaryConversionScenarioProbabilityMeasurementInputMember_8e580454-3d5a-40b0-9305-3f14274a64ab" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_InitialPriceLimitMeasurementInputMember_97cd79a9-ff97-4b9e-b274-7208f63efd6a" xlink:href="abvx-20251231.xsd#abvx_InitialPriceLimitMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_697203e3-7f0c-40ea-8d83-109b440d3879" xlink:to="loc_abvx_InitialPriceLimitMeasurementInputMember_97cd79a9-ff97-4b9e-b274-7208f63efd6a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EarlyRedemptionAmountMeasurementInputMember_3a4b60bb-0150-4de0-8714-8789c4478718" xlink:href="abvx-20251231.xsd#abvx_EarlyRedemptionAmountMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_697203e3-7f0c-40ea-8d83-109b440d3879" xlink:to="loc_abvx_EarlyRedemptionAmountMeasurementInputMember_3a4b60bb-0150-4de0-8714-8789c4478718" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_HistoricalVolatilityForSharesMeasurementInputMember_c3cc9604-dd17-4414-847b-0c1d72b3eeb9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_HistoricalVolatilityForSharesMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_697203e3-7f0c-40ea-8d83-109b440d3879" xlink:to="loc_ifrs-full_HistoricalVolatilityForSharesMeasurementInputMember_c3cc9604-dd17-4414-847b-0c1d72b3eeb9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CreditSpreadMeasurementInputMember_5c66691a-1f09-44d9-b7e7-5b3af049283c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CreditSpreadMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_697203e3-7f0c-40ea-8d83-109b440d3879" xlink:to="loc_ifrs-full_CreditSpreadMeasurementInputMember_5c66691a-1f09-44d9-b7e7-5b3af049283c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RiskFreeInterestRateMeasurementInputMember_077bf4c7-df59-47d8-8e79-4eba84787eb5" xlink:href="abvx-20251231.xsd#abvx_RiskFreeInterestRateMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_697203e3-7f0c-40ea-8d83-109b440d3879" xlink:to="loc_abvx_RiskFreeInterestRateMeasurementInputMember_077bf4c7-df59-47d8-8e79-4eba84787eb5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_431db341-8e53-4721-9728-c8f1aa9432b8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfFinancialLiabilitiesTable_24ccb8fc-d0dc-4297-bc7e-6503ac2e3749" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_431db341-8e53-4721-9728-c8f1aa9432b8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_431db341-8e53-4721-9728-c8f1aa9432b8_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_431db341-8e53-4721-9728-c8f1aa9432b8" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_431db341-8e53-4721-9728-c8f1aa9432b8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_c180f943-6c01-45af-9948-018bd227344c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_431db341-8e53-4721-9728-c8f1aa9432b8" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_c180f943-6c01-45af-9948-018bd227344c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_MonteCarloModelIFRSMember_a9f21e00-afe2-4118-b799-89e8c14e4834" xlink:href="abvx-20251231.xsd#abvx_MonteCarloModelIFRSMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_c180f943-6c01-45af-9948-018bd227344c" xlink:to="loc_abvx_MonteCarloModelIFRSMember_a9f21e00-afe2-4118-b799-89e8c14e4834" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfConvertibleNotesOutstanding_19aa7b31-69b0-4d2d-8675-67a4744929c9" xlink:href="abvx-20251231.xsd#abvx_NumberOfConvertibleNotesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfFinancialLiabilitiesLineItems_d337f439-0521-46ad-80b2-95d6ff073461" xlink:to="loc_abvx_NumberOfConvertibleNotesOutstanding_19aa7b31-69b0-4d2d-8675-67a4744929c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NotionalAmount_693d56dd-8700-4a39-a61a-bb29f1d5b721" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfFinancialLiabilitiesLineItems_d337f439-0521-46ad-80b2-95d6ff073461" xlink:to="loc_ifrs-full_NotionalAmount_693d56dd-8700-4a39-a61a-bb29f1d5b721" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_SignificantUnobservableInputLiabilities_8afef000-f6ed-40e4-8215-bd8e9a831773" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SignificantUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfFinancialLiabilitiesLineItems_d337f439-0521-46ad-80b2-95d6ff073461" xlink:to="loc_ifrs-full_SignificantUnobservableInputLiabilities_8afef000-f6ed-40e4-8215-bd8e9a831773" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AggregateFairValueConvertibleNotes_076facea-3161-41c0-9724-90f5624af683" xlink:href="abvx-20251231.xsd#abvx_AggregateFairValueConvertibleNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfFinancialLiabilitiesLineItems_d337f439-0521-46ad-80b2-95d6ff073461" xlink:to="loc_abvx_AggregateFairValueConvertibleNotes_076facea-3161-41c0-9724-90f5624af683" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesKreos1Details" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesKreos1Details"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesKreos1Details" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_d79094d2-00f4-4224-9d4b-0bfd16a7f8f4" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_d79094d2-00f4-4224-9d4b-0bfd16a7f8f4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_019c56eb-f87d-70b1-b721-9421cfb2104b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_d79094d2-00f4-4224-9d4b-0bfd16a7f8f4" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_019c56eb-f87d-70b1-b721-9421cfb2104b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019c56eb-f87d-70b1-b721-9421cfb2104b_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019c56eb-f87d-70b1-b721-9421cfb2104b" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019c56eb-f87d-70b1-b721-9421cfb2104b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019c56eb-f87d-766c-b6fa-a7df6fee600f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019c56eb-f87d-70b1-b721-9421cfb2104b" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019c56eb-f87d-766c-b6fa-a7df6fee600f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos1Member_019c56eb-f87d-7b6e-b66a-662dc4eefe28" xlink:href="abvx-20251231.xsd#abvx_Kreos1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019c56eb-f87d-766c-b6fa-a7df6fee600f" xlink:to="loc_abvx_Kreos1Member_019c56eb-f87d-7b6e-b66a-662dc4eefe28" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos1NonConvertibleBondLoansMember_019c56eb-f87d-7d54-b4eb-46985852d6e1" xlink:href="abvx-20251231.xsd#abvx_Kreos1NonConvertibleBondLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019c56eb-f87d-766c-b6fa-a7df6fee600f" xlink:to="loc_abvx_Kreos1NonConvertibleBondLoansMember_019c56eb-f87d-7d54-b4eb-46985852d6e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos1ConvertibleBondLoansMember_019c56eb-f87d-7ce2-9196-e78aaf4dfed1" xlink:href="abvx-20251231.xsd#abvx_Kreos1ConvertibleBondLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019c56eb-f87d-766c-b6fa-a7df6fee600f" xlink:to="loc_abvx_Kreos1ConvertibleBondLoansMember_019c56eb-f87d-7ce2-9196-e78aaf4dfed1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos1ConvertibleBondLoansTrancheBMember_019c56eb-f87d-720d-8a4d-6f944d66b548" xlink:href="abvx-20251231.xsd#abvx_Kreos1ConvertibleBondLoansTrancheBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019c56eb-f87d-766c-b6fa-a7df6fee600f" xlink:to="loc_abvx_Kreos1ConvertibleBondLoansTrancheBMember_019c56eb-f87d-720d-8a4d-6f944d66b548" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos12BondLoansMember_019c56eb-f87d-7d7e-ab9c-2f0ff9d99960" xlink:href="abvx-20251231.xsd#abvx_Kreos12BondLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019c56eb-f87d-766c-b6fa-a7df6fee600f" xlink:to="loc_abvx_Kreos12BondLoansMember_019c56eb-f87d-7d7e-ab9c-2f0ff9d99960" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos1ConvertibleBondLoansTrancheAMember_019c56eb-f87d-7566-a4c1-132a80d333c2" xlink:href="abvx-20251231.xsd#abvx_Kreos1ConvertibleBondLoansTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019c56eb-f87d-766c-b6fa-a7df6fee600f" xlink:to="loc_abvx_Kreos1ConvertibleBondLoansTrancheAMember_019c56eb-f87d-7566-a4c1-132a80d333c2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsAxis_019c56eb-f87d-7849-831d-cb3c5a041e9b" xlink:href="abvx-20251231.xsd#abvx_WarrantsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_d79094d2-00f4-4224-9d4b-0bfd16a7f8f4" xlink:to="loc_abvx_WarrantsAxis_019c56eb-f87d-7849-831d-cb3c5a041e9b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsDomain_019c56eb-f87d-7849-831d-cb3c5a041e9b_default" xlink:href="abvx-20251231.xsd#abvx_WarrantsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_WarrantsAxis_019c56eb-f87d-7849-831d-cb3c5a041e9b" xlink:to="loc_abvx_WarrantsDomain_019c56eb-f87d-7849-831d-cb3c5a041e9b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsDomain_019c56eb-f87d-72a1-9713-b8aa41ded0a8" xlink:href="abvx-20251231.xsd#abvx_WarrantsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_WarrantsAxis_019c56eb-f87d-7849-831d-cb3c5a041e9b" xlink:to="loc_abvx_WarrantsDomain_019c56eb-f87d-72a1-9713-b8aa41ded0a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosABSAMember_019c56eb-f87d-7ad1-aac5-5c14dc91c7ec" xlink:href="abvx-20251231.xsd#abvx_KreosABSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_WarrantsDomain_019c56eb-f87d-72a1-9713-b8aa41ded0a8" xlink:to="loc_abvx_KreosABSAMember_019c56eb-f87d-7ad1-aac5-5c14dc91c7ec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosBBSAMember_019c56eb-f87d-7ff6-97b4-72952900d8b9" xlink:href="abvx-20251231.xsd#abvx_KreosBBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_WarrantsDomain_019c56eb-f87d-72a1-9713-b8aa41ded0a8" xlink:to="loc_abvx_KreosBBSAMember_019c56eb-f87d-7ff6-97b4-72952900d8b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosABBSAMember_019c56eb-f87d-72a5-b4cc-4e60ca083296" xlink:href="abvx-20251231.xsd#abvx_KreosABBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_WarrantsDomain_019c56eb-f87d-72a1-9713-b8aa41ded0a8" xlink:to="loc_abvx_KreosABBSAMember_019c56eb-f87d-72a5-b4cc-4e60ca083296" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalAxis_019c56eb-f87d-76bd-80e9-f3899b2326cb" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_d79094d2-00f4-4224-9d4b-0bfd16a7f8f4" xlink:to="loc_ifrs-full_ClassesOfShareCapitalAxis_019c56eb-f87d-76bd-80e9-f3899b2326cb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalDomain_019c56eb-f87d-76bd-80e9-f3899b2326cb_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfShareCapitalAxis_019c56eb-f87d-76bd-80e9-f3899b2326cb" xlink:to="loc_ifrs-full_ClassesOfShareCapitalDomain_019c56eb-f87d-76bd-80e9-f3899b2326cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfShareCapitalDomain_019c56eb-f87d-76c7-9ca3-8e65b983c033" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfShareCapitalAxis_019c56eb-f87d-76bd-80e9-f3899b2326cb" xlink:to="loc_ifrs-full_ClassesOfShareCapitalDomain_019c56eb-f87d-76c7-9ca3-8e65b983c033" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OrdinarySharesMember_019c56eb-f87d-7eb2-b71e-0be9fdb8a8ad" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OrdinarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfShareCapitalDomain_019c56eb-f87d-76c7-9ca3-8e65b983c033" xlink:to="loc_ifrs-full_OrdinarySharesMember_019c56eb-f87d-7eb2-b71e-0be9fdb8a8ad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsMaximumBorrowingCapacity_019c56eb-f87d-7b79-9d5e-46585ad1474b" xlink:href="abvx-20251231.xsd#abvx_BorrowingsMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:to="loc_abvx_BorrowingsMaximumBorrowingCapacity_019c56eb-f87d-7b79-9d5e-46585ad1474b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsNumberOfTranches_019c56eb-f87d-7292-b04e-9dce2756154f" xlink:href="abvx-20251231.xsd#abvx_BorrowingsNumberOfTranches"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:to="loc_abvx_BorrowingsNumberOfTranches_019c56eb-f87d-7292-b04e-9dce2756154f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsMaximumBorrowingCapacityPerTranche_019c56eb-f87d-76ff-9d46-7fd2cb5c368f" xlink:href="abvx-20251231.xsd#abvx_BorrowingsMaximumBorrowingCapacityPerTranche"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:to="loc_abvx_BorrowingsMaximumBorrowingCapacityPerTranche_019c56eb-f87d-76ff-9d46-7fd2cb5c368f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants_019c56eb-f87d-7cb6-8ad4-dde1695e1564" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:to="loc_abvx_IncreaseDecreaseInNumberOfSharesIssuedThroughExerciseOfShareWarrants_019c56eb-f87d-7cb6-8ad4-dde1695e1564" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RepaymentsOfConvertibleLoansNotes_019c56eb-f87d-735c-958a-e4575c0d7fc9" xlink:href="abvx-20251231.xsd#abvx_RepaymentsOfConvertibleLoansNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:to="loc_abvx_RepaymentsOfConvertibleLoansNotes_019c56eb-f87d-735c-958a-e4575c0d7fc9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GainLossArisingFromDifferenceBetweenCarryingAmountOfFinancialLiabilityExtinguishedAndConsiderationPaid_019c56eb-f87d-7b77-8087-8c3c2ddd67f9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GainLossArisingFromDifferenceBetweenCarryingAmountOfFinancialLiabilityExtinguishedAndConsiderationPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:to="loc_ifrs-full_GainLossArisingFromDifferenceBetweenCarryingAmountOfFinancialLiabilityExtinguishedAndConsiderationPaid_019c56eb-f87d-7b77-8087-8c3c2ddd67f9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfShareWarrantsIssued_019c56eb-f87d-7a8c-ae11-16b4b4a8cccb" xlink:href="abvx-20251231.xsd#abvx_NumberOfShareWarrantsIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:to="loc_abvx_NumberOfShareWarrantsIssued_019c56eb-f87d-7a8c-ae11-16b4b4a8cccb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ShareWarrantsSubscriptionPricePerShare_019c56eb-f87d-7a8b-98f2-7cb08c0af0b2" xlink:href="abvx-20251231.xsd#abvx_ShareWarrantsSubscriptionPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:to="loc_abvx_ShareWarrantsSubscriptionPricePerShare_019c56eb-f87d-7a8b-98f2-7cb08c0af0b2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfSharesPerShareWarrant_019c56eb-f87d-790e-a524-e604f3dc9eb8" xlink:href="abvx-20251231.xsd#abvx_NumberOfSharesPerShareWarrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:to="loc_abvx_NumberOfSharesPerShareWarrant_019c56eb-f87d-790e-a524-e604f3dc9eb8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ExercisePriceShareOptionsGranted2019_019c56eb-f87d-71d6-aec2-4e27a502366a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ExercisePriceShareOptionsGranted2019"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:to="loc_ifrs-full_ExercisePriceShareOptionsGranted2019_019c56eb-f87d-71d6-aec2-4e27a502366a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfOtherShareWarrantsRepurchased_019c56eb-f87d-7453-8fbd-478dc64cf59e" xlink:href="abvx-20251231.xsd#abvx_NumberOfOtherShareWarrantsRepurchased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:to="loc_abvx_NumberOfOtherShareWarrantsRepurchased_019c56eb-f87d-7453-8fbd-478dc64cf59e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfOtherShareWarrantsConverted_019c56eb-f87d-7dcb-b1c5-d482103a18e0" xlink:href="abvx-20251231.xsd#abvx_NumberOfOtherShareWarrantsConverted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:to="loc_abvx_NumberOfOtherShareWarrantsConverted_019c56eb-f87d-7dcb-b1c5-d482103a18e0" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughExerciseOfWarrantsEquity_019c56eb-f87d-750c-b5a8-df791801209a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughExerciseOfWarrantsEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56eb-f87d-7f70-8309-6889b8b13ee2" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughExerciseOfWarrantsEquity_019c56eb-f87d-750c-b5a8-df791801209a" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesDisclosureofthemaindataandassumptionsKreosBSADetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesDisclosureofthemaindataandassumptionsKreosBSADetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesDisclosureofthemaindataandassumptionsKreosBSADetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfWarrantsArrangementsLineItems_e022a2b0-7017-48b3-90a4-1464412daac2" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfWarrantsArrangementsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfWarrantsArrangementsTable_94ab92ee-a296-44e7-a3af-51bb336d2413" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfWarrantsArrangementsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsLineItems_e022a2b0-7017-48b3-90a4-1464412daac2" xlink:to="loc_abvx_DisclosureOfWarrantsArrangementsTable_94ab92ee-a296-44e7-a3af-51bb336d2413" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsAxis_31c19bc1-4aaf-4928-9af4-e7da6ee3ffea" xlink:href="abvx-20251231.xsd#abvx_WarrantsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsTable_94ab92ee-a296-44e7-a3af-51bb336d2413" xlink:to="loc_abvx_WarrantsAxis_31c19bc1-4aaf-4928-9af4-e7da6ee3ffea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsDomain_31c19bc1-4aaf-4928-9af4-e7da6ee3ffea_default" xlink:href="abvx-20251231.xsd#abvx_WarrantsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_WarrantsAxis_31c19bc1-4aaf-4928-9af4-e7da6ee3ffea" xlink:to="loc_abvx_WarrantsDomain_31c19bc1-4aaf-4928-9af4-e7da6ee3ffea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_WarrantsDomain_0d8c9e4f-3f9b-4273-843c-0397e2b7e9ef" xlink:href="abvx-20251231.xsd#abvx_WarrantsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_WarrantsAxis_31c19bc1-4aaf-4928-9af4-e7da6ee3ffea" xlink:to="loc_abvx_WarrantsDomain_0d8c9e4f-3f9b-4273-843c-0397e2b7e9ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosABSAMember_c3aaac39-29d8-49c6-9dc5-df378d5c4b3e" xlink:href="abvx-20251231.xsd#abvx_KreosABSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_WarrantsDomain_0d8c9e4f-3f9b-4273-843c-0397e2b7e9ef" xlink:to="loc_abvx_KreosABSAMember_c3aaac39-29d8-49c6-9dc5-df378d5c4b3e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosBBSAMember_510ac62c-6b44-41cb-92fb-bd9d6841d527" xlink:href="abvx-20251231.xsd#abvx_KreosBBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_WarrantsDomain_0d8c9e4f-3f9b-4273-843c-0397e2b7e9ef" xlink:to="loc_abvx_KreosBBSAMember_510ac62c-6b44-41cb-92fb-bd9d6841d527" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsAxis_df9006e3-6bdf-47aa-b426-dca35a705327" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsTable_94ab92ee-a296-44e7-a3af-51bb336d2413" xlink:to="loc_ifrs-full_UnobservableInputsAxis_df9006e3-6bdf-47aa-b426-dca35a705327" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_df9006e3-6bdf-47aa-b426-dca35a705327_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_UnobservableInputsAxis_df9006e3-6bdf-47aa-b426-dca35a705327" xlink:to="loc_ifrs-full_UnobservableInputsDomain_df9006e3-6bdf-47aa-b426-dca35a705327_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_a3a41e96-1515-4d6c-90c4-5ef60ef6ae60" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_UnobservableInputsAxis_df9006e3-6bdf-47aa-b426-dca35a705327" xlink:to="loc_ifrs-full_UnobservableInputsDomain_a3a41e96-1515-4d6c-90c4-5ef60ef6ae60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExercisePricePerShareMeasurementInputMember_815b56cc-d1ab-4e9e-af58-f1ecf1711104" xlink:href="abvx-20251231.xsd#abvx_ExercisePricePerShareMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_a3a41e96-1515-4d6c-90c4-5ef60ef6ae60" xlink:to="loc_abvx_ExercisePricePerShareMeasurementInputMember_815b56cc-d1ab-4e9e-af58-f1ecf1711104" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SharePriceMeasurementInputMember_a62b75ca-3c5f-4ac4-a39a-c9e6012742c1" xlink:href="abvx-20251231.xsd#abvx_SharePriceMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_a3a41e96-1515-4d6c-90c4-5ef60ef6ae60" xlink:to="loc_abvx_SharePriceMeasurementInputMember_a62b75ca-3c5f-4ac4-a39a-c9e6012742c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_729bd8a8-d893-4e34-bf75-824b0d930139" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsTable_94ab92ee-a296-44e7-a3af-51bb336d2413" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_729bd8a8-d893-4e34-bf75-824b0d930139" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_729bd8a8-d893-4e34-bf75-824b0d930139_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_729bd8a8-d893-4e34-bf75-824b0d930139" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_729bd8a8-d893-4e34-bf75-824b0d930139_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_8f43a780-eaf3-4628-8a4a-76d325daeff8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_729bd8a8-d893-4e34-bf75-824b0d930139" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_8f43a780-eaf3-4628-8a4a-76d325daeff8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OptionPricingModelMember_0acfedaf-fd25-46d9-9ba9-0c7f2e597426" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OptionPricingModelMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_8f43a780-eaf3-4628-8a4a-76d325daeff8" xlink:to="loc_ifrs-full_OptionPricingModelMember_0acfedaf-fd25-46d9-9ba9-0c7f2e597426" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfWarrantsOutstanding_708db23d-c912-4aa1-a9b4-fe2c6171b978" xlink:href="abvx-20251231.xsd#abvx_NumberOfWarrantsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsLineItems_e022a2b0-7017-48b3-90a4-1464412daac2" xlink:to="loc_abvx_NumberOfWarrantsOutstanding_708db23d-c912-4aa1-a9b4-fe2c6171b978" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_SignificantUnobservableInputLiabilities_2420e6e4-9a23-4e9f-931d-3b5f8f1d7d44" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SignificantUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsLineItems_e022a2b0-7017-48b3-90a4-1464412daac2" xlink:to="loc_ifrs-full_SignificantUnobservableInputLiabilities_2420e6e4-9a23-4e9f-931d-3b5f8f1d7d44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AggregateFairValueOtherEquityInstrumentsOutstanding_862bf3c3-dd15-45e5-bc2e-e10347da9258" xlink:href="abvx-20251231.xsd#abvx_AggregateFairValueOtherEquityInstrumentsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfWarrantsArrangementsLineItems_e022a2b0-7017-48b3-90a4-1464412daac2" xlink:to="loc_abvx_AggregateFairValueOtherEquityInstrumentsOutstanding_862bf3c3-dd15-45e5-bc2e-e10347da9258" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesKreos2Details" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesKreos2Details"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesKreos2Details" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f5-9d35-7bf9-9931-9c1fc6ceebaf" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_44d45666-828b-41c2-b946-3c4604f70488" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f5-9d35-7bf9-9931-9c1fc6ceebaf" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_44d45666-828b-41c2-b946-3c4604f70488" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_019c56f5-9d35-7331-aedd-bdecfb838337" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_44d45666-828b-41c2-b946-3c4604f70488" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_019c56f5-9d35-7331-aedd-bdecfb838337" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019c56f5-9d35-7331-aedd-bdecfb838337_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019c56f5-9d35-7331-aedd-bdecfb838337" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019c56f5-9d35-7331-aedd-bdecfb838337_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019c56f5-9d35-7b94-b36a-52aeabf359aa" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019c56f5-9d35-7331-aedd-bdecfb838337" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019c56f5-9d35-7b94-b36a-52aeabf359aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos2Member_019c56f5-9d35-7e06-940a-c9a3fd5ab0d5" xlink:href="abvx-20251231.xsd#abvx_Kreos2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019c56f5-9d35-7b94-b36a-52aeabf359aa" xlink:to="loc_abvx_Kreos2Member_019c56f5-9d35-7e06-940a-c9a3fd5ab0d5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos2TrancheAMember_019c56f5-9d35-7b8e-875a-fee1818ac367" xlink:href="abvx-20251231.xsd#abvx_Kreos2TrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019c56f5-9d35-7b94-b36a-52aeabf359aa" xlink:to="loc_abvx_Kreos2TrancheAMember_019c56f5-9d35-7b8e-875a-fee1818ac367" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos2TrancheBMember_019c56f5-9d35-7e86-a797-6d3324ac2855" xlink:href="abvx-20251231.xsd#abvx_Kreos2TrancheBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019c56f5-9d35-7b94-b36a-52aeabf359aa" xlink:to="loc_abvx_Kreos2TrancheBMember_019c56f5-9d35-7e86-a797-6d3324ac2855" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos1ConvertibleBondLoansTrancheBMember_019c56f5-9d35-79d1-968f-00f21ab12342" xlink:href="abvx-20251231.xsd#abvx_Kreos1ConvertibleBondLoansTrancheBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019c56f5-9d35-7b94-b36a-52aeabf359aa" xlink:to="loc_abvx_Kreos1ConvertibleBondLoansTrancheBMember_019c56f5-9d35-79d1-968f-00f21ab12342" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NotionalAmount_019c56f5-9d35-7d42-9584-a17aaebd06d3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f5-9d35-7bf9-9931-9c1fc6ceebaf" xlink:to="loc_ifrs-full_NotionalAmount_019c56f5-9d35-7d42-9584-a17aaebd06d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsNumberOfTranches_019c56f5-9d35-7017-a1ec-120e54ab2246" xlink:href="abvx-20251231.xsd#abvx_BorrowingsNumberOfTranches"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f5-9d35-7bf9-9931-9c1fc6ceebaf" xlink:to="loc_abvx_BorrowingsNumberOfTranches_019c56f5-9d35-7017-a1ec-120e54ab2246" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsAdditionalTrancheAmount_019c56f5-9d35-7f60-9de7-5cc983486576" xlink:href="abvx-20251231.xsd#abvx_BorrowingsAdditionalTrancheAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f5-9d35-7bf9-9931-9c1fc6ceebaf" xlink:to="loc_abvx_BorrowingsAdditionalTrancheAmount_019c56f5-9d35-7f60-9de7-5cc983486576" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RepaymentsOfConvertibleLoansNotes_019c56f5-9d35-70d1-be55-1596967dc743" xlink:href="abvx-20251231.xsd#abvx_RepaymentsOfConvertibleLoansNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f5-9d35-7bf9-9931-9c1fc6ceebaf" xlink:to="loc_abvx_RepaymentsOfConvertibleLoansNotes_019c56f5-9d35-70d1-be55-1596967dc743" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesOCEANEDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesOCEANEDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesOCEANEDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_feb8fe6e-32b2-4c27-b55a-59e41b01fc45" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_feb8fe6e-32b2-4c27-b55a-59e41b01fc45" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_019c56f4-89fe-7e02-87a0-ffb7ca2821c4" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_feb8fe6e-32b2-4c27-b55a-59e41b01fc45" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_019c56f4-89fe-7e02-87a0-ffb7ca2821c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019c56f4-89fe-7e02-87a0-ffb7ca2821c4_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019c56f4-89fe-7e02-87a0-ffb7ca2821c4" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019c56f4-89fe-7e02-87a0-ffb7ca2821c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019c56f4-89fe-7e80-84c6-0194a64aa635" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019c56f4-89fe-7e02-87a0-ffb7ca2821c4" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019c56f4-89fe-7e80-84c6-0194a64aa635" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OCEANEMember_019c56f4-89fe-7479-a5f4-07fa01f3d5d1" xlink:href="abvx-20251231.xsd#abvx_OCEANEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019c56f4-89fe-7e80-84c6-0194a64aa635" xlink:to="loc_abvx_OCEANEMember_019c56f4-89fe-7479-a5f4-07fa01f3d5d1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RemeasurementPeriodAxis_019c56f4-89fe-73d8-a605-d79f5761ebba" xlink:href="abvx-20251231.xsd#abvx_RemeasurementPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_feb8fe6e-32b2-4c27-b55a-59e41b01fc45" xlink:to="loc_abvx_RemeasurementPeriodAxis_019c56f4-89fe-73d8-a605-d79f5761ebba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RemeasurementPeriodDomain_019c56f4-89fe-73d8-a605-d79f5761ebba_default" xlink:href="abvx-20251231.xsd#abvx_RemeasurementPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_RemeasurementPeriodAxis_019c56f4-89fe-73d8-a605-d79f5761ebba" xlink:to="loc_abvx_RemeasurementPeriodDomain_019c56f4-89fe-73d8-a605-d79f5761ebba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RemeasurementPeriodDomain_019c56f4-89fe-731b-83a5-5a752c3dd36c" xlink:href="abvx-20251231.xsd#abvx_RemeasurementPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_RemeasurementPeriodAxis_019c56f4-89fe-73d8-a605-d79f5761ebba" xlink:to="loc_abvx_RemeasurementPeriodDomain_019c56f4-89fe-731b-83a5-5a752c3dd36c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_After18MonthsMember_019c56f4-89fe-7b48-bdf7-2c7ccf456bac" xlink:href="abvx-20251231.xsd#abvx_After18MonthsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_RemeasurementPeriodDomain_019c56f4-89fe-731b-83a5-5a752c3dd36c" xlink:to="loc_abvx_After18MonthsMember_019c56f4-89fe-7b48-bdf7-2c7ccf456bac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_After24MonthsMember_019c56f4-89fe-78fe-a722-d7a2e0f8dabd" xlink:href="abvx-20251231.xsd#abvx_After24MonthsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_RemeasurementPeriodDomain_019c56f4-89fe-731b-83a5-5a752c3dd36c" xlink:to="loc_abvx_After24MonthsMember_019c56f4-89fe-78fe-a722-d7a2e0f8dabd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_After36MonthsMember_019c56f4-89fe-76cd-a5e4-339c00c555fb" xlink:href="abvx-20251231.xsd#abvx_After36MonthsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_RemeasurementPeriodDomain_019c56f4-89fe-731b-83a5-5a752c3dd36c" xlink:to="loc_abvx_After36MonthsMember_019c56f4-89fe-76cd-a5e4-339c00c555fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019c56f4-89fe-7bdb-8c68-f89d080bb082" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_feb8fe6e-32b2-4c27-b55a-59e41b01fc45" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019c56f4-89fe-7bdb-8c68-f89d080bb082" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019c56f4-89fe-7bdb-8c68-f89d080bb082_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019c56f4-89fe-7bdb-8c68-f89d080bb082" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019c56f4-89fe-7bdb-8c68-f89d080bb082_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019c56f4-89fe-7e2a-8d8d-8614c09eefd8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019c56f4-89fe-7bdb-8c68-f89d080bb082" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019c56f4-89fe-7e2a-8d8d-8614c09eefd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OCEANEMember_019c56f4-89fe-761e-bd49-a28a646847aa" xlink:href="abvx-20251231.xsd#abvx_OCEANEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019c56f4-89fe-7e2a-8d8d-8614c09eefd8" xlink:to="loc_abvx_OCEANEMember_019c56f4-89fe-761e-bd49-a28a646847aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsAxis_019c56f4-89fe-7868-80bb-aad993484364" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_feb8fe6e-32b2-4c27-b55a-59e41b01fc45" xlink:to="loc_ifrs-full_UnobservableInputsAxis_019c56f4-89fe-7868-80bb-aad993484364" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_019c56f4-89fe-7868-80bb-aad993484364_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_UnobservableInputsAxis_019c56f4-89fe-7868-80bb-aad993484364" xlink:to="loc_ifrs-full_UnobservableInputsDomain_019c56f4-89fe-7868-80bb-aad993484364_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_019c56f4-89fe-79d4-b762-f3da1e11b194" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_UnobservableInputsAxis_019c56f4-89fe-7868-80bb-aad993484364" xlink:to="loc_ifrs-full_UnobservableInputsDomain_019c56f4-89fe-79d4-b762-f3da1e11b194" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_HistoricalVolatilityForSharesMeasurementInputMember_019c56f4-89fe-73bf-9359-6d7a7d7f9636" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_HistoricalVolatilityForSharesMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019c56f4-89fe-79d4-b762-f3da1e11b194" xlink:to="loc_ifrs-full_HistoricalVolatilityForSharesMeasurementInputMember_019c56f4-89fe-73bf-9359-6d7a7d7f9636" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CreditSpreadMeasurementInputMember_019c56f4-89fe-7ee7-ac5b-ec486aa07f2c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CreditSpreadMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019c56f4-89fe-79d4-b762-f3da1e11b194" xlink:to="loc_ifrs-full_CreditSpreadMeasurementInputMember_019c56f4-89fe-7ee7-ac5b-ec486aa07f2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SharePriceMeasurementInputMember_019c56f4-89fe-7360-ab3a-064074067392" xlink:href="abvx-20251231.xsd#abvx_SharePriceMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019c56f4-89fe-79d4-b762-f3da1e11b194" xlink:to="loc_abvx_SharePriceMeasurementInputMember_019c56f4-89fe-7360-ab3a-064074067392" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RiskFreeInterestRateMeasurementInputMember_019c56f4-89fe-7d19-9cc2-1f8e0848f4b1" xlink:href="abvx-20251231.xsd#abvx_RiskFreeInterestRateMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019c56f4-89fe-79d4-b762-f3da1e11b194" xlink:to="loc_abvx_RiskFreeInterestRateMeasurementInputMember_019c56f4-89fe-7d19-9cc2-1f8e0848f4b1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_019c56f4-89fe-710e-8842-d28121d41df5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_feb8fe6e-32b2-4c27-b55a-59e41b01fc45" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_019c56f4-89fe-710e-8842-d28121d41df5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_019c56f4-89fe-710e-8842-d28121d41df5_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_019c56f4-89fe-710e-8842-d28121d41df5" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_019c56f4-89fe-710e-8842-d28121d41df5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_019c56f4-89fe-772f-996e-7d28a81f340e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis_019c56f4-89fe-710e-8842-d28121d41df5" xlink:to="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_019c56f4-89fe-772f-996e-7d28a81f340e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_MonteCarloModelIFRSMember_019c56f4-89fe-7afb-9ba2-6d4679defc30" xlink:href="abvx-20251231.xsd#abvx_MonteCarloModelIFRSMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ValuationTechniquesUsedInFairValueMeasurementDomain_019c56f4-89fe-772f-996e-7d28a81f340e" xlink:to="loc_abvx_MonteCarloModelIFRSMember_019c56f4-89fe-7afb-9ba2-6d4679defc30" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ProceedsFromIssuingSharesAndConvertibleLoansNotes_019c56f4-89fe-7828-be5a-f3525c08cf0f" xlink:href="abvx-20251231.xsd#abvx_ProceedsFromIssuingSharesAndConvertibleLoansNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:to="loc_abvx_ProceedsFromIssuingSharesAndConvertibleLoansNotes_019c56f4-89fe-7828-be5a-f3525c08cf0f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease_019c56f4-89fe-77a0-82da-bf2bc678e0f2" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:to="loc_abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease_019c56f4-89fe-77a0-82da-bf2bc678e0f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EquityIssuanceSubscriptionPricePerShare_019c56f4-89fe-7758-a880-e84014382883" xlink:href="abvx-20251231.xsd#abvx_EquityIssuanceSubscriptionPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:to="loc_abvx_EquityIssuanceSubscriptionPricePerShare_019c56f4-89fe-7758-a880-e84014382883" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProceedsFromIssuingShares_019c56f4-89fe-77e1-9697-0b8c2c106419" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProceedsFromIssuingShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:to="loc_ifrs-full_ProceedsFromIssuingShares_019c56f4-89fe-77e1-9697-0b8c2c106419" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NetProceedsFromConvertibleLoansNotes_019c56f4-89fe-758e-a9bd-3681ab066299" xlink:href="abvx-20251231.xsd#abvx_NetProceedsFromConvertibleLoansNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:to="loc_abvx_NetProceedsFromConvertibleLoansNotes_019c56f4-89fe-758e-a9bd-3681ab066299" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConversionPriceAdjustmentPeriod_019c56f4-89fe-70cc-b4eb-04feb9e73a0e" xlink:href="abvx-20251231.xsd#abvx_ConversionPriceAdjustmentPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:to="loc_abvx_ConversionPriceAdjustmentPeriod_019c56f4-89fe-70cc-b4eb-04feb9e73a0e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_SignificantUnobservableInputLiabilities_019c56f4-89fe-7078-b1dc-fbbd8514817c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SignificantUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:to="loc_ifrs-full_SignificantUnobservableInputLiabilities_019c56f4-89fe-7078-b1dc-fbbd8514817c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AggregateFairValueConvertibleNotes_019c56f4-89fe-782b-a659-6e4ada9daefc" xlink:href="abvx-20251231.xsd#abvx_AggregateFairValueConvertibleNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:to="loc_abvx_AggregateFairValueConvertibleNotes_019c56f4-89fe-782b-a659-6e4ada9daefc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019c56f4-89fe-7da1-b5d7-a6fca9c276e0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:to="loc_ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019c56f4-89fe-7da1-b5d7-a6fca9c276e0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AmountOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019c56f4-89fe-7197-bf4f-33a65f6be7b8" xlink:href="abvx-20251231.xsd#abvx_AmountOfReasonablyPossibleIncreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:to="loc_abvx_AmountOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019c56f4-89fe-7197-bf4f-33a65f6be7b8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputAssets_019c56f4-89fe-7591-af78-1a3413155698" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:to="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputAssets_019c56f4-89fe-7591-af78-1a3413155698" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RepaymentsOfConvertibleLoansNotes_019c56f4-89fe-77c0-9355-239d34bfcbf3" xlink:href="abvx-20251231.xsd#abvx_RepaymentsOfConvertibleLoansNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:to="loc_abvx_RepaymentsOfConvertibleLoansNotes_019c56f4-89fe-77c0-9355-239d34bfcbf3" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GainLossArisingFromDifferenceBetweenCarryingAmountOfFinancialLiabilityExtinguishedAndConsiderationPaid_019c56f4-89fe-7a0c-977e-aa206502b6a7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GainLossArisingFromDifferenceBetweenCarryingAmountOfFinancialLiabilityExtinguishedAndConsiderationPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019c56f4-89fe-7f94-9f8f-aab28713fd5c" xlink:to="loc_ifrs-full_GainLossArisingFromDifferenceBetweenCarryingAmountOfFinancialLiabilityExtinguishedAndConsiderationPaid_019c56f4-89fe-7a0c-977e-aa206502b6a7" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesStateguaranteedloanPGEDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesStateguaranteedloanPGEDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesStateguaranteedloanPGEDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_47c997b2-20b4-4ccb-ba02-014aa5dacbcf" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_12c38cae-fae0-467d-aca8-c83d9af261fa" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_47c997b2-20b4-4ccb-ba02-014aa5dacbcf" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_12c38cae-fae0-467d-aca8-c83d9af261fa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_cb9cd544-3883-4089-8111-b8f93c9b1c54" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_12c38cae-fae0-467d-aca8-c83d9af261fa" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_cb9cd544-3883-4089-8111-b8f93c9b1c54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_cb9cd544-3883-4089-8111-b8f93c9b1c54_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_cb9cd544-3883-4089-8111-b8f93c9b1c54" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_cb9cd544-3883-4089-8111-b8f93c9b1c54_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_2c0fa645-5dfd-4659-900a-b18dc776400e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_cb9cd544-3883-4089-8111-b8f93c9b1c54" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_2c0fa645-5dfd-4659-900a-b18dc776400e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PretGarantiParLEtatPGEMember_3df1dc0a-138a-4bce-988d-0ff37c982b30" xlink:href="abvx-20251231.xsd#abvx_PretGarantiParLEtatPGEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_2c0fa645-5dfd-4659-900a-b18dc776400e" xlink:to="loc_abvx_PretGarantiParLEtatPGEMember_3df1dc0a-138a-4bce-988d-0ff37c982b30" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsMaturityTerm_a857c880-a58a-46a0-9dd1-30e29abc33c2" xlink:href="abvx-20251231.xsd#abvx_BorrowingsMaturityTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_47c997b2-20b4-4ccb-ba02-014aa5dacbcf" xlink:to="loc_abvx_BorrowingsMaturityTerm_a857c880-a58a-46a0-9dd1-30e29abc33c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsInterestRate_d7042f2b-09be-4f04-aa01-a17b7ce9b1cd" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_47c997b2-20b4-4ccb-ba02-014aa5dacbcf" xlink:to="loc_ifrs-full_BorrowingsInterestRate_d7042f2b-09be-4f04-aa01-a17b7ce9b1cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsMaturityExtensionTerm_1549860c-9773-401b-9bd0-c58db631edfe" xlink:href="abvx-20251231.xsd#abvx_BorrowingsMaturityExtensionTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_47c997b2-20b4-4ccb-ba02-014aa5dacbcf" xlink:to="loc_abvx_BorrowingsMaturityExtensionTerm_1549860c-9773-401b-9bd0-c58db631edfe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsMaturityDeferralPeriod_a3557aa1-a742-4229-911e-8c6a98b794de" xlink:href="abvx-20251231.xsd#abvx_BorrowingsMaturityDeferralPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_47c997b2-20b4-4ccb-ba02-014aa5dacbcf" xlink:to="loc_abvx_BorrowingsMaturityDeferralPeriod_a3557aa1-a742-4229-911e-8c6a98b794de" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsStateGuaranteedPremium_720299d8-31e4-41a7-8d42-453505d93e53" xlink:href="abvx-20251231.xsd#abvx_BorrowingsStateGuaranteedPremium"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_47c997b2-20b4-4ccb-ba02-014aa5dacbcf" xlink:to="loc_abvx_BorrowingsStateGuaranteedPremium_720299d8-31e4-41a7-8d42-453505d93e53" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RevenueFromGovernmentGrants_55a9fd97-506f-4b35-9e54-74f2fd49e4d2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RevenueFromGovernmentGrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_47c997b2-20b4-4ccb-ba02-014aa5dacbcf" xlink:to="loc_ifrs-full_RevenueFromGovernmentGrants_55a9fd97-506f-4b35-9e54-74f2fd49e4d2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RepaymentsOfBorrowingsClassifiedAsFinancingActivities_019cfd00-dead-7593-831e-7f92c598802c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RepaymentsOfBorrowingsClassifiedAsFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_47c997b2-20b4-4ccb-ba02-014aa5dacbcf" xlink:to="loc_ifrs-full_RepaymentsOfBorrowingsClassifiedAsFinancingActivities_019cfd00-dead-7593-831e-7f92c598802c" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesDisclosureofconditionaladvancesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesDisclosureofconditionaladvancesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesDisclosureofconditionaladvancesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_d5c1e78b-a09f-4b20-800a-7dceefeb27eb" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_0dde3b7b-9ebd-4ff9-b341-9eaa156746e0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_d5c1e78b-a09f-4b20-800a-7dceefeb27eb" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_0dde3b7b-9ebd-4ff9-b341-9eaa156746e0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_1512a780-f378-40ad-91d5-26d86d28a163" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_0dde3b7b-9ebd-4ff9-b341-9eaa156746e0" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_1512a780-f378-40ad-91d5-26d86d28a163" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_1512a780-f378-40ad-91d5-26d86d28a163_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_1512a780-f378-40ad-91d5-26d86d28a163" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_1512a780-f378-40ad-91d5-26d86d28a163_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_74400510-9cfd-44f5-a78e-314dd5058b2e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_1512a780-f378-40ad-91d5-26d86d28a163" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_74400510-9cfd-44f5-a78e-314dd5058b2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RNPVIRConditionalAdvanceBPIMember_56ea95fa-14f2-4d54-b87c-7860015747a1" xlink:href="abvx-20251231.xsd#abvx_RNPVIRConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_74400510-9cfd-44f5-a78e-314dd5058b2e" xlink:to="loc_abvx_RNPVIRConditionalAdvanceBPIMember_56ea95fa-14f2-4d54-b87c-7860015747a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CARENAConditionalAdvanceBPIMember_40906cfa-579f-4069-a20d-cfc599e68fd2" xlink:href="abvx-20251231.xsd#abvx_CARENAConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_74400510-9cfd-44f5-a78e-314dd5058b2e" xlink:to="loc_abvx_CARENAConditionalAdvanceBPIMember_40906cfa-579f-4069-a20d-cfc599e68fd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EbolaConditionalAdvanceBPIMember_85a3eb3c-1921-4d36-959e-6e64c423e464" xlink:href="abvx-20251231.xsd#abvx_EbolaConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_74400510-9cfd-44f5-a78e-314dd5058b2e" xlink:to="loc_abvx_EbolaConditionalAdvanceBPIMember_85a3eb3c-1921-4d36-959e-6e64c423e464" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConditionalAdvances_dd46eddd-0d44-4d65-a6e8-34740071014e" xlink:href="abvx-20251231.xsd#abvx_ConditionalAdvances"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_d5c1e78b-a09f-4b20-800a-7dceefeb27eb" xlink:to="loc_abvx_ConditionalAdvances_dd46eddd-0d44-4d65-a6e8-34740071014e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesConditionaladvancesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesConditionaladvancesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesConditionaladvancesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_fe4daff4-1733-4154-a906-16629ff5fa3c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_6f4460f0-d988-4d01-bd8e-2757931c12b5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_fe4daff4-1733-4154-a906-16629ff5fa3c" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_6f4460f0-d988-4d01-bd8e-2757931c12b5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_8d892f5a-c9b4-493d-9fb7-2b9116e7141c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_6f4460f0-d988-4d01-bd8e-2757931c12b5" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_8d892f5a-c9b4-493d-9fb7-2b9116e7141c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_8d892f5a-c9b4-493d-9fb7-2b9116e7141c_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_8d892f5a-c9b4-493d-9fb7-2b9116e7141c" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_8d892f5a-c9b4-493d-9fb7-2b9116e7141c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_f92c6b63-42de-4e4d-893e-81e1bb6ba342" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_8d892f5a-c9b4-493d-9fb7-2b9116e7141c" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_f92c6b63-42de-4e4d-893e-81e1bb6ba342" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RNPVIRConditionalAdvanceBPIMember_a23d6645-428f-46ae-8e37-1f6350f2ca59" xlink:href="abvx-20251231.xsd#abvx_RNPVIRConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_f92c6b63-42de-4e4d-893e-81e1bb6ba342" xlink:to="loc_abvx_RNPVIRConditionalAdvanceBPIMember_a23d6645-428f-46ae-8e37-1f6350f2ca59" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CARENAConditionalAdvanceBPIMember_81c2ca5d-6b5a-42ca-8d2e-e475ac1ce075" xlink:href="abvx-20251231.xsd#abvx_CARENAConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_f92c6b63-42de-4e4d-893e-81e1bb6ba342" xlink:to="loc_abvx_CARENAConditionalAdvanceBPIMember_81c2ca5d-6b5a-42ca-8d2e-e475ac1ce075" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EbolaConditionalAdvanceBPIMember_d3494ba1-9878-43c3-83d7-62d67d8d1744" xlink:href="abvx-20251231.xsd#abvx_EbolaConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_f92c6b63-42de-4e4d-893e-81e1bb6ba342" xlink:to="loc_abvx_EbolaConditionalAdvanceBPIMember_d3494ba1-9878-43c3-83d7-62d67d8d1744" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherFinancialLiabilitiesMaximumDrawdownCapacity_93586da5-d530-417d-874c-903f538f7c6b" xlink:href="abvx-20251231.xsd#abvx_OtherFinancialLiabilitiesMaximumDrawdownCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_fe4daff4-1733-4154-a906-16629ff5fa3c" xlink:to="loc_abvx_OtherFinancialLiabilitiesMaximumDrawdownCapacity_93586da5-d530-417d-874c-903f538f7c6b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ProceedsFromConditionalAdvances_17ecd6f5-a1e6-474b-940d-f287c15aff9e" xlink:href="abvx-20251231.xsd#abvx_ProceedsFromConditionalAdvances"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_fe4daff4-1733-4154-a906-16629ff5fa3c" xlink:to="loc_abvx_ProceedsFromConditionalAdvances_17ecd6f5-a1e6-474b-940d-f287c15aff9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RepaymentOfExcessConditionalAdvancesClaimed_844a21c4-b1e7-4d98-8a33-65ada243005f" xlink:href="abvx-20251231.xsd#abvx_RepaymentOfExcessConditionalAdvancesClaimed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_fe4daff4-1733-4154-a906-16629ff5fa3c" xlink:to="loc_abvx_RepaymentOfExcessConditionalAdvancesClaimed_844a21c4-b1e7-4d98-8a33-65ada243005f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PercentageOfConditionalAdvancesWaived_5e106c9c-ecf7-4311-9ba0-9931f66878af" xlink:href="abvx-20251231.xsd#abvx_PercentageOfConditionalAdvancesWaived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_fe4daff4-1733-4154-a906-16629ff5fa3c" xlink:to="loc_abvx_PercentageOfConditionalAdvancesWaived_5e106c9c-ecf7-4311-9ba0-9931f66878af" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConditionalAdvances_2b90c9cb-550a-40f5-a520-85b294bc5642" xlink:href="abvx-20251231.xsd#abvx_ConditionalAdvances"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_fe4daff4-1733-4154-a906-16629ff5fa3c" xlink:to="loc_abvx_ConditionalAdvances_2b90c9cb-550a-40f5-a520-85b294bc5642" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RevenueFromGovernmentGrants_24982f23-2603-4d52-93fa-2e9fb3654c62" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RevenueFromGovernmentGrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_fe4daff4-1733-4154-a906-16629ff5fa3c" xlink:to="loc_ifrs-full_RevenueFromGovernmentGrants_24982f23-2603-4d52-93fa-2e9fb3654c62" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesLeaseliabilitiesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesLeaseliabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesLeaseliabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfLeaseLiabilitiesLineItems_3ce3eef7-3f85-4c91-a089-66af04cd3665" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfLeaseLiabilitiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfLeaseLiabilitiesTable_90179b54-69e9-496c-ab74-817e7d9e4f63" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfLeaseLiabilitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_abvx_DisclosureOfLeaseLiabilitiesLineItems_3ce3eef7-3f85-4c91-a089-66af04cd3665" xlink:to="loc_abvx_DisclosureOfLeaseLiabilitiesTable_90179b54-69e9-496c-ab74-817e7d9e4f63" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfContractsAxis_e33b131f-937a-409e-a626-a69c8b74c07d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfContractsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfLeaseLiabilitiesTable_90179b54-69e9-496c-ab74-817e7d9e4f63" xlink:to="loc_ifrs-full_TypesOfContractsAxis_e33b131f-937a-409e-a626-a69c8b74c07d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfContractsDomain_e33b131f-937a-409e-a626-a69c8b74c07d_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfContractsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfContractsAxis_e33b131f-937a-409e-a626-a69c8b74c07d" xlink:to="loc_ifrs-full_TypesOfContractsDomain_e33b131f-937a-409e-a626-a69c8b74c07d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfContractsDomain_97674617-d0ab-490d-9c5c-c5e74c323ea0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfContractsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfContractsAxis_e33b131f-937a-409e-a626-a69c8b74c07d" xlink:to="loc_ifrs-full_TypesOfContractsDomain_97674617-d0ab-490d-9c5c-c5e74c323ea0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_LeaseFacilitiesParisMember_4a89ae34-eeca-4181-98e3-51d148e535dd" xlink:href="abvx-20251231.xsd#abvx_LeaseFacilitiesParisMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfContractsDomain_97674617-d0ab-490d-9c5c-c5e74c323ea0" xlink:to="loc_abvx_LeaseFacilitiesParisMember_4a89ae34-eeca-4181-98e3-51d148e535dd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_LeaseFacilitiesBostonMember_a1cbcce2-3e76-414d-b6a3-b69badbe6c25" xlink:href="abvx-20251231.xsd#abvx_LeaseFacilitiesBostonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfContractsDomain_97674617-d0ab-490d-9c5c-c5e74c323ea0" xlink:to="loc_abvx_LeaseFacilitiesBostonMember_a1cbcce2-3e76-414d-b6a3-b69badbe6c25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_LeaseFacilitiesMontpellierMember_4bfd11f5-80a5-41e6-9c49-00f26b6a25f5" xlink:href="abvx-20251231.xsd#abvx_LeaseFacilitiesMontpellierMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfContractsDomain_97674617-d0ab-490d-9c5c-c5e74c323ea0" xlink:to="loc_abvx_LeaseFacilitiesMontpellierMember_4bfd11f5-80a5-41e6-9c49-00f26b6a25f5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_LeaseFacilitiesMember_edbd71fc-7f11-4c0a-a766-7488ae6c73f7" xlink:href="abvx-20251231.xsd#abvx_LeaseFacilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfContractsDomain_97674617-d0ab-490d-9c5c-c5e74c323ea0" xlink:to="loc_abvx_LeaseFacilitiesMember_edbd71fc-7f11-4c0a-a766-7488ae6c73f7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeAxis_f12f6201-73a8-40c9-ae35-e515234d081f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfLeaseLiabilitiesTable_90179b54-69e9-496c-ab74-817e7d9e4f63" xlink:to="loc_ifrs-full_RangeAxis_f12f6201-73a8-40c9-ae35-e515234d081f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_f12f6201-73a8-40c9-ae35-e515234d081f_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_RangeAxis_f12f6201-73a8-40c9-ae35-e515234d081f" xlink:to="loc_ifrs-full_RangeDomain_f12f6201-73a8-40c9-ae35-e515234d081f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_e403825c-8b2c-42d0-a5de-829d6bda500d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_RangeAxis_f12f6201-73a8-40c9-ae35-e515234d081f" xlink:to="loc_ifrs-full_RangeDomain_e403825c-8b2c-42d0-a5de-829d6bda500d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_f50f22cf-387f-4388-85cb-015842be2b90" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_e403825c-8b2c-42d0-a5de-829d6bda500d" xlink:to="loc_srt_MinimumMember_f50f22cf-387f-4388-85cb-015842be2b90" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_6eb94a93-26f8-4c9d-9ce3-599ca2d178de" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_e403825c-8b2c-42d0-a5de-829d6bda500d" xlink:to="loc_srt_MaximumMember_6eb94a93-26f8-4c9d-9ce3-599ca2d178de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_LeaseDurationPeriod_1e0c8955-8a6b-46b2-b4a4-39c1d979646b" xlink:href="abvx-20251231.xsd#abvx_LeaseDurationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfLeaseLiabilitiesLineItems_3ce3eef7-3f85-4c91-a089-66af04cd3665" xlink:to="loc_abvx_LeaseDurationPeriod_1e0c8955-8a6b-46b2-b4a4-39c1d979646b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_LeaseTacitRenewalPeriod_0898cda7-4946-485d-9d23-09e011157c89" xlink:href="abvx-20251231.xsd#abvx_LeaseTacitRenewalPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfLeaseLiabilitiesLineItems_3ce3eef7-3f85-4c91-a089-66af04cd3665" xlink:to="loc_abvx_LeaseTacitRenewalPeriod_0898cda7-4946-485d-9d23-09e011157c89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_LeaseBreakClausePeriod_c333363e-1cf8-45ba-98ef-5c3c79cd4f2f" xlink:href="abvx-20251231.xsd#abvx_LeaseBreakClausePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfLeaseLiabilitiesLineItems_3ce3eef7-3f85-4c91-a089-66af04cd3665" xlink:to="loc_abvx_LeaseBreakClausePeriod_c333363e-1cf8-45ba-98ef-5c3c79cd4f2f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DecreaseInLeaseLiabilitiesThroughModificationOfTerm_dd1fe94e-4176-41bb-b74e-3eb8b59215c8" xlink:href="abvx-20251231.xsd#abvx_DecreaseInLeaseLiabilitiesThroughModificationOfTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfLeaseLiabilitiesLineItems_3ce3eef7-3f85-4c91-a089-66af04cd3665" xlink:to="loc_abvx_DecreaseInLeaseLiabilitiesThroughModificationOfTerm_dd1fe94e-4176-41bb-b74e-3eb8b59215c8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_LeaseExtensionPeriod_29f0aec0-12b0-4493-8a9f-36a9eb40b020" xlink:href="abvx-20251231.xsd#abvx_LeaseExtensionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfLeaseLiabilitiesLineItems_3ce3eef7-3f85-4c91-a089-66af04cd3665" xlink:to="loc_abvx_LeaseExtensionPeriod_29f0aec0-12b0-4493-8a9f-36a9eb40b020" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_LeaseLiabilityPercentageOfTotal_b600d7c7-fa0c-45e0-b93a-d68222509182" xlink:href="abvx-20251231.xsd#abvx_LeaseLiabilityPercentageOfTotal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfLeaseLiabilitiesLineItems_3ce3eef7-3f85-4c91-a089-66af04cd3665" xlink:to="loc_abvx_LeaseLiabilityPercentageOfTotal_b600d7c7-fa0c-45e0-b93a-d68222509182" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExpenseOnLeaseLiabilities_763d7c17-55c2-4c27-a09a-c8ac6b304787" xlink:href="abvx-20251231.xsd#abvx_ExpenseOnLeaseLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfLeaseLiabilitiesLineItems_3ce3eef7-3f85-4c91-a089-66af04cd3665" xlink:to="loc_abvx_ExpenseOnLeaseLiabilities_763d7c17-55c2-4c27-a09a-c8ac6b304787" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DepreciationExpenseLease_d5c85315-27d7-4af5-b1d7-2c80a9708152" xlink:href="abvx-20251231.xsd#abvx_DepreciationExpenseLease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfLeaseLiabilitiesLineItems_3ce3eef7-3f85-4c91-a089-66af04cd3665" xlink:to="loc_abvx_DepreciationExpenseLease_d5c85315-27d7-4af5-b1d7-2c80a9708152" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_InterestExpenseOnLeaseLiabilities_703d05b3-f0eb-4df3-86e6-7b59cf150ca9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_InterestExpenseOnLeaseLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfLeaseLiabilitiesLineItems_3ce3eef7-3f85-4c91-a089-66af04cd3665" xlink:to="loc_ifrs-full_InterestExpenseOnLeaseLiabilities_703d05b3-f0eb-4df3-86e6-7b59cf150ca9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExpenseRelatingToShortTermLeasesAndLowValueAssetsForWhichRecognitionExemptionHasBeenUsed_cf18d510-0fb4-4a37-b8c4-9dd3b2e62f02" xlink:href="abvx-20251231.xsd#abvx_ExpenseRelatingToShortTermLeasesAndLowValueAssetsForWhichRecognitionExemptionHasBeenUsed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfLeaseLiabilitiesLineItems_3ce3eef7-3f85-4c91-a089-66af04cd3665" xlink:to="loc_abvx_ExpenseRelatingToShortTermLeasesAndLowValueAssetsForWhichRecognitionExemptionHasBeenUsed_cf18d510-0fb4-4a37-b8c4-9dd3b2e62f02" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesRoyaltycertificatesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesRoyaltycertificatesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesRoyaltycertificatesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_29aeafb0-99bb-41d3-a620-494d837525ee" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_29aeafb0-99bb-41d3-a620-494d837525ee" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019bffa7-38ad-7881-aa13-56ccfbd47f07" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_29aeafb0-99bb-41d3-a620-494d837525ee" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019bffa7-38ad-7881-aa13-56ccfbd47f07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bffa7-38ad-7881-aa13-56ccfbd47f07_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019bffa7-38ad-7881-aa13-56ccfbd47f07" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bffa7-38ad-7881-aa13-56ccfbd47f07_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bffa7-38ad-7163-bcce-d128c8e34d9d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019bffa7-38ad-7881-aa13-56ccfbd47f07" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bffa7-38ad-7163-bcce-d128c8e34d9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RoyaltyCertificatesMember_019bffa7-38ad-756a-af6e-4f182497d06f" xlink:href="abvx-20251231.xsd#abvx_RoyaltyCertificatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019bffa7-38ad-7163-bcce-d128c8e34d9d" xlink:to="loc_abvx_RoyaltyCertificatesMember_019bffa7-38ad-756a-af6e-4f182497d06f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ComponentsOfEquityAxis_019bffa7-38ad-74e1-924b-0fdfae1eff24" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_29aeafb0-99bb-41d3-a620-494d837525ee" xlink:to="loc_ifrs-full_ComponentsOfEquityAxis_019bffa7-38ad-74e1-924b-0fdfae1eff24" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ComponentsOfEquityDomain_019bffa7-38ad-74e1-924b-0fdfae1eff24_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ComponentsOfEquityAxis_019bffa7-38ad-74e1-924b-0fdfae1eff24" xlink:to="loc_ifrs-full_ComponentsOfEquityDomain_019bffa7-38ad-74e1-924b-0fdfae1eff24_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ComponentsOfEquityDomain_019bffa7-38ad-7be3-950a-e9c64fac0d26" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ComponentsOfEquityAxis_019bffa7-38ad-74e1-924b-0fdfae1eff24" xlink:to="loc_ifrs-full_ComponentsOfEquityDomain_019bffa7-38ad-7be3-950a-e9c64fac0d26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_SharePremiumMember_019bffa7-38ad-742c-ae99-e1b725a7138e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SharePremiumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ComponentsOfEquityDomain_019bffa7-38ad-7be3-950a-e9c64fac0d26" xlink:to="loc_ifrs-full_SharePremiumMember_019bffa7-38ad-742c-ae99-e1b725a7138e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis_019bffa7-38ad-7647-b202-c388f5137ebd" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_29aeafb0-99bb-41d3-a620-494d837525ee" xlink:to="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis_019bffa7-38ad-7647-b202-c388f5137ebd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_019bffa7-38ad-7647-b202-c388f5137ebd_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis_019bffa7-38ad-7647-b202-c388f5137ebd" xlink:to="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_019bffa7-38ad-7647-b202-c388f5137ebd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_019bffa7-38ad-7e8b-8a6f-cf9bf4adbea9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis_019bffa7-38ad-7647-b202-c388f5137ebd" xlink:to="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_019bffa7-38ad-7e8b-8a6f-cf9bf4adbea9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RoyaltyCertificatesMember_019bffa7-38ad-7a64-9a71-82af63b506b4" xlink:href="abvx-20251231.xsd#abvx_RoyaltyCertificatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_019bffa7-38ad-7e8b-8a6f-cf9bf4adbea9" xlink:to="loc_abvx_RoyaltyCertificatesMember_019bffa7-38ad-7a64-9a71-82af63b506b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsAxis_019bffa7-9b9e-7b9c-b770-f7b82339cae6" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_29aeafb0-99bb-41d3-a620-494d837525ee" xlink:to="loc_ifrs-full_UnobservableInputsAxis_019bffa7-9b9e-7b9c-b770-f7b82339cae6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_019bffa7-9b9e-7b9c-b770-f7b82339cae6_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_UnobservableInputsAxis_019bffa7-9b9e-7b9c-b770-f7b82339cae6" xlink:to="loc_ifrs-full_UnobservableInputsDomain_019bffa7-9b9e-7b9c-b770-f7b82339cae6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnobservableInputsDomain_019bffa7-9b9e-7a0c-a352-5876d295342b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnobservableInputsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_UnobservableInputsAxis_019bffa7-9b9e-7b9c-b770-f7b82339cae6" xlink:to="loc_ifrs-full_UnobservableInputsDomain_019bffa7-9b9e-7a0c-a352-5876d295342b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ProbabilityOfSuccessMeasurementInputMember_019bffa7-9b9e-7c7f-afed-329a082d1291" xlink:href="abvx-20251231.xsd#abvx_ProbabilityOfSuccessMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bffa7-9b9e-7a0c-a352-5876d295342b" xlink:to="loc_abvx_ProbabilityOfSuccessMeasurementInputMember_019bffa7-9b9e-7c7f-afed-329a082d1291" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PeakPenetrationMeasurementInputMember_019bffa7-9b9e-79f1-a4ae-cdfe6557697d" xlink:href="abvx-20251231.xsd#abvx_PeakPenetrationMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bffa7-9b9e-7a0c-a352-5876d295342b" xlink:to="loc_abvx_PeakPenetrationMeasurementInputMember_019bffa7-9b9e-79f1-a4ae-cdfe6557697d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DiscountRateMeasurementInputMember_019bffa7-d5df-7c58-aefe-54d001ca1ce9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DiscountRateMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bffa7-9b9e-7a0c-a352-5876d295342b" xlink:to="loc_ifrs-full_DiscountRateMeasurementInputMember_019bffa7-d5df-7c58-aefe-54d001ca1ce9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_WeightedAverageCostOfCapitalMeasurementInputMember_019bffa8-5859-7c48-ac7a-c5e9a15ba52a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_WeightedAverageCostOfCapitalMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bffa7-9b9e-7a0c-a352-5876d295342b" xlink:to="loc_ifrs-full_WeightedAverageCostOfCapitalMeasurementInputMember_019bffa8-5859-7c48-ac7a-c5e9a15ba52a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SharePriceMeasurementInputMember_019bffa8-5859-7f7c-bd51-2fbd6b84bd4b" xlink:href="abvx-20251231.xsd#abvx_SharePriceMeasurementInputMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_UnobservableInputsDomain_019bffa7-9b9e-7a0c-a352-5876d295342b" xlink:to="loc_abvx_SharePriceMeasurementInputMember_019bffa8-5859-7f7c-bd51-2fbd6b84bd4b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NotionalAmount_019bffa7-38ad-7d14-896c-5ddfb393aae8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_ifrs-full_NotionalAmount_019bffa7-38ad-7d14-896c-5ddfb393aae8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherLiabilitiesNumberOfTransactions_019bffa7-38ad-721a-a548-7b128cfd9db5" xlink:href="abvx-20251231.xsd#abvx_OtherLiabilitiesNumberOfTransactions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_OtherLiabilitiesNumberOfTransactions_019bffa7-38ad-721a-a548-7b128cfd9db5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IssueOfEquity_019bffa7-38ad-7e94-9d92-605ae4e29f41" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IssueOfEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_ifrs-full_IssueOfEquity_019bffa7-38ad-7e94-9d92-605ae4e29f41" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease_019bffa7-38ad-7564-bdd7-846176f57c71" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_IncreaseDecreaseInNumberOfOrdinarySharesIssuedThroughCapitalIncrease_019bffa7-38ad-7564-bdd7-846176f57c71" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ParValuePerShare_019bffa7-38ad-7e09-8581-cde59c963300" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ParValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_ifrs-full_ParValuePerShare_019bffa7-38ad-7e09-8581-cde59c963300" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EquityIssuanceSubscriptionPricePerShare_019bffa7-38ad-7810-a567-aa8a1f8680f5" xlink:href="abvx-20251231.xsd#abvx_EquityIssuanceSubscriptionPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_EquityIssuanceSubscriptionPricePerShare_019bffa7-38ad-7810-a567-aa8a1f8680f5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NetProceedsFromSaleOfRoyaltyCertificates_019bffa7-38ad-7fe4-ae90-8fed5a98a807" xlink:href="abvx-20251231.xsd#abvx_NetProceedsFromSaleOfRoyaltyCertificates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_NetProceedsFromSaleOfRoyaltyCertificates_019bffa7-38ad-7fe4-ae90-8fed5a98a807" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RoyaltyCertificatePercentageOfFutureSales_019bffa7-38ad-73fa-9c4f-452751285f40" xlink:href="abvx-20251231.xsd#abvx_RoyaltyCertificatePercentageOfFutureSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_RoyaltyCertificatePercentageOfFutureSales_019bffa7-38ad-73fa-9c4f-452751285f40" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RoyaltyCertificateMaximumAmount_019bffa7-38ad-73b8-8eee-db78ab00ecd0" xlink:href="abvx-20251231.xsd#abvx_RoyaltyCertificateMaximumAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_RoyaltyCertificateMaximumAmount_019bffa7-38ad-73b8-8eee-db78ab00ecd0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ShareIssueRelatedCost_019bffa7-38ad-7227-bc08-bb6da64a836d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ShareIssueRelatedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_ifrs-full_ShareIssueRelatedCost_019bffa7-38ad-7227-bc08-bb6da64a836d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RoyaltyCertificatesEIR_019bffa7-38ad-77fe-945d-ae258c83a886" xlink:href="abvx-20251231.xsd#abvx_RoyaltyCertificatesEIR"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_RoyaltyCertificatesEIR_019bffa7-38ad-77fe-945d-ae258c83a886" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseThroughAmortizationCostRemeasurementLiabilitiesArisingFromFinancingActivities_019bffa7-38ad-712a-ad7e-d61049b171cd" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseThroughAmortizationCostRemeasurementLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_IncreaseDecreaseThroughAmortizationCostRemeasurementLiabilitiesArisingFromFinancingActivities_019bffa7-38ad-712a-ad7e-d61049b171cd" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_InterestExpenseOnRoyaltyCertificatesIncludingTheUnwindingOfDiscount_019cc355-1afa-75a6-b67b-c756b4814935" xlink:href="abvx-20251231.xsd#abvx_InterestExpenseOnRoyaltyCertificatesIncludingTheUnwindingOfDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_InterestExpenseOnRoyaltyCertificatesIncludingTheUnwindingOfDiscount_019cc355-1afa-75a6-b67b-c756b4814935" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_UnwindingOfDiscountOnRoyalties_019bffa7-38ad-7d1f-969c-4879e029870f" xlink:href="abvx-20251231.xsd#abvx_UnwindingOfDiscountOnRoyalties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_UnwindingOfDiscountOnRoyalties_019bffa7-38ad-7d1f-969c-4879e029870f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bffa7-9b9e-7aa2-8dad-d3d373ac91c3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bffa7-9b9e-7aa2-8dad-d3d373ac91c3" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInCarryingValueDueToReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bffa7-9b9e-7c62-9256-61085e1a7395" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInCarryingValueDueToReasonablyPossibleIncreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_IncreaseDecreaseInCarryingValueDueToReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bffa7-9b9e-7c62-9256-61085e1a7395" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PercentageOfReasonablyPossibleDecreaseInUnobservableInputLiabilities_019bffa7-9b9e-7fe4-9b1b-44ece0a3f912" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PercentageOfReasonablyPossibleDecreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_ifrs-full_PercentageOfReasonablyPossibleDecreaseInUnobservableInputLiabilities_019bffa7-9b9e-7fe4-9b1b-44ece0a3f912" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInCarryingValueDueToReasonablyPossibleDecreaseInUnobservableInputLiabilities_019bffa7-9b9e-7282-b713-e584e8928c63" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInCarryingValueDueToReasonablyPossibleDecreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_IncreaseDecreaseInCarryingValueDueToReasonablyPossibleDecreaseInUnobservableInputLiabilities_019bffa7-9b9e-7282-b713-e584e8928c63" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_FinancialLiabilitiesAtFairValue_019bffa7-d5df-7ae5-be28-907032db5d3b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FinancialLiabilitiesAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_ifrs-full_FinancialLiabilitiesAtFairValue_019bffa7-d5df-7ae5-be28-907032db5d3b" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_UnobservableInputLiabilitiesDiscountRate_019cfd0f-9f4a-733f-bef7-84fa815ccf7f" xlink:href="abvx-20251231.xsd#abvx_UnobservableInputLiabilitiesDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_UnobservableInputLiabilitiesDiscountRate_019cfd0f-9f4a-733f-bef7-84fa815ccf7f" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AmountOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bffa8-5859-780e-928d-33a887c1b159" xlink:href="abvx-20251231.xsd#abvx_AmountOfReasonablyPossibleIncreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_AmountOfReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bffa8-5859-780e-928d-33a887c1b159" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bffa8-5859-7b0b-932b-d4022ee61264" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleIncreaseInUnobservableInputLiabilities_019bffa8-5859-7b0b-932b-d4022ee61264" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AmountOfReasonablyPossibleDecreaseInUnobservableInputLiabilities_019bffa8-5859-7763-82c3-105310a28740" xlink:href="abvx-20251231.xsd#abvx_AmountOfReasonablyPossibleDecreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_abvx_AmountOfReasonablyPossibleDecreaseInUnobservableInputLiabilities_019bffa8-5859-7763-82c3-105310a28740" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleDecreaseInUnobservableInputLiabilities_019bffa8-5859-7122-83b6-3f32d58cec9a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleDecreaseInUnobservableInputLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_019bffa7-38ad-7c0c-8ddf-b8d1f1b55258" xlink:to="loc_ifrs-full_IncreaseDecreaseInFairValueMeasurementDueToReasonablyPossibleDecreaseInUnobservableInputLiabilities_019bffa8-5859-7122-83b6-3f32d58cec9a" xlink:type="arc" order="23"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesDisclosureofreconciliationofliabilitiesarisingfromfinancingactivitiesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesDisclosureofreconciliationofliabilitiesarisingfromfinancingactivitiesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesDisclosureofreconciliationofliabilitiesarisingfromfinancingactivitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesTable_fd50bf14-1f81-44a8-856c-5728ed8fe292" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesTable_fd50bf14-1f81-44a8-856c-5728ed8fe292" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis_b9a6a222-0ab5-4235-a39c-2f44b045df5b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesTable_fd50bf14-1f81-44a8-856c-5728ed8fe292" xlink:to="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis_b9a6a222-0ab5-4235-a39c-2f44b045df5b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_b9a6a222-0ab5-4235-a39c-2f44b045df5b_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis_b9a6a222-0ab5-4235-a39c-2f44b045df5b" xlink:to="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_b9a6a222-0ab5-4235-a39c-2f44b045df5b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_a6de3721-e5dd-4c7a-b311-d842bb5dcbfa" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesAxis_b9a6a222-0ab5-4235-a39c-2f44b045df5b" xlink:to="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_a6de3721-e5dd-4c7a-b311-d842bb5dcbfa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos12BondLoansMember_2444bc7c-0cc7-41b6-9cb7-6492a736b687" xlink:href="abvx-20251231.xsd#abvx_Kreos12BondLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_a6de3721-e5dd-4c7a-b311-d842bb5dcbfa" xlink:to="loc_abvx_Kreos12BondLoansMember_2444bc7c-0cc7-41b6-9cb7-6492a736b687" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OCEANEMember_de55bdc7-bdb6-4afd-85ad-d365ff2be4db" xlink:href="abvx-20251231.xsd#abvx_OCEANEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_a6de3721-e5dd-4c7a-b311-d842bb5dcbfa" xlink:to="loc_abvx_OCEANEMember_de55bdc7-bdb6-4afd-85ad-d365ff2be4db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheAMember_e96e63c0-f448-4116-afdb-65b6840c369c" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_a6de3721-e5dd-4c7a-b311-d842bb5dcbfa" xlink:to="loc_abvx_KreosClaretFinancingTrancheAMember_e96e63c0-f448-4116-afdb-65b6840c369c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_Kreos1ClaretBondLoansMember_f0f39668-ae05-4710-84d4-6bd0d5c6708f" xlink:href="abvx-20251231.xsd#abvx_Kreos1ClaretBondLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_a6de3721-e5dd-4c7a-b311-d842bb5dcbfa" xlink:to="loc_abvx_Kreos1ClaretBondLoansMember_f0f39668-ae05-4710-84d4-6bd0d5c6708f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_HeightsConvertibleNotesMember_6f8f511e-b6a9-4e12-b939-0940a66f37c0" xlink:href="abvx-20251231.xsd#abvx_HeightsConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_a6de3721-e5dd-4c7a-b311-d842bb5dcbfa" xlink:to="loc_abvx_HeightsConvertibleNotesMember_6f8f511e-b6a9-4e12-b939-0940a66f37c0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PretGarantiParLEtatPGEMember_08633a4a-8a55-42ae-a17b-fceaeaba9199" xlink:href="abvx-20251231.xsd#abvx_PretGarantiParLEtatPGEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_a6de3721-e5dd-4c7a-b311-d842bb5dcbfa" xlink:to="loc_abvx_PretGarantiParLEtatPGEMember_08633a4a-8a55-42ae-a17b-fceaeaba9199" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConditionalAdvancesMember_4effc3a7-7520-4256-943f-728033e84f49" xlink:href="abvx-20251231.xsd#abvx_ConditionalAdvancesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_a6de3721-e5dd-4c7a-b311-d842bb5dcbfa" xlink:to="loc_abvx_ConditionalAdvancesMember_4effc3a7-7520-4256-943f-728033e84f49" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LeaseLiabilitiesMember_9e2f4a58-ca9e-441f-9314-6328394f38b7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LeaseLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_a6de3721-e5dd-4c7a-b311-d842bb5dcbfa" xlink:to="loc_ifrs-full_LeaseLiabilitiesMember_9e2f4a58-ca9e-441f-9314-6328394f38b7" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RoyaltyCertificatesMember_541b547f-1bca-4e7e-b52b-3f03327f0cd5" xlink:href="abvx-20251231.xsd#abvx_RoyaltyCertificatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_LiabilitiesArisingFromFinancingActivitiesDomain_a6de3721-e5dd-4c7a-b311-d842bb5dcbfa" xlink:to="loc_abvx_RoyaltyCertificatesMember_541b547f-1bca-4e7e-b52b-3f03327f0cd5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LiabilitiesArisingFromFinancingActivities_77655021-90d9-445e-b733-fb009709bdd3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_ifrs-full_LiabilitiesArisingFromFinancingActivities_77655021-90d9-445e-b733-fb009709bdd3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseThroughProceedsLiabilitiesArisingFromFinancingActivities_32b1894e-aca4-46e0-91c9-fd8ab718d3ed" xlink:href="abvx-20251231.xsd#abvx_IncreaseThroughProceedsLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_abvx_IncreaseThroughProceedsLiabilitiesArisingFromFinancingActivities_32b1894e-aca4-46e0-91c9-fd8ab718d3ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DecreaseThroughRepaymentsLiabilitiesArisingFromFinancingActivities_f83a13ea-01b7-42fd-93ec-056e02845d7d" xlink:href="abvx-20251231.xsd#abvx_DecreaseThroughRepaymentsLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_abvx_DecreaseThroughRepaymentsLiabilitiesArisingFromFinancingActivities_f83a13ea-01b7-42fd-93ec-056e02845d7d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DecreaseThroughInterestPaidLiabilitiesArisingFromFinancingActivities_927733f9-50fa-45f4-92f5-46c6683f864d" xlink:href="abvx-20251231.xsd#abvx_DecreaseThroughInterestPaidLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_abvx_DecreaseThroughInterestPaidLiabilitiesArisingFromFinancingActivities_927733f9-50fa-45f4-92f5-46c6683f864d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseThroughClassificationOfEmbeddedDerivativesAsSeparateFinancialInstrumentsLiabilitiesArisingFromFinancingActivities_9fbf257d-7ea5-4e1b-ad97-4cfc6aa897d9" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseThroughClassificationOfEmbeddedDerivativesAsSeparateFinancialInstrumentsLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_abvx_IncreaseDecreaseThroughClassificationOfEmbeddedDerivativesAsSeparateFinancialInstrumentsLiabilitiesArisingFromFinancingActivities_9fbf257d-7ea5-4e1b-ad97-4cfc6aa897d9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseThroughGainLossOnRecognitionDerecognitionLiabilitiesArisingFromFinancingActivities_3b4cd96f-b533-4ab5-a5dc-65dc7ad9cb27" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseThroughGainLossOnRecognitionDerecognitionLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_abvx_IncreaseDecreaseThroughGainLossOnRecognitionDerecognitionLiabilitiesArisingFromFinancingActivities_3b4cd96f-b533-4ab5-a5dc-65dc7ad9cb27" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughOtherChangesLiabilitiesArisingFromFinancingActivities_43fa501c-3d10-446b-b9bc-bee4ee9c9de7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughOtherChangesLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughOtherChangesLiabilitiesArisingFromFinancingActivities_43fa501c-3d10-446b-b9bc-bee4ee9c9de7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseThroughRecognitionOfEarnOutLiabilityLiabilitiesArisingFromFinancingActivities_349580da-da7b-4521-aefd-89513f8bc6e6" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseThroughRecognitionOfEarnOutLiabilityLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_abvx_IncreaseDecreaseThroughRecognitionOfEarnOutLiabilityLiabilitiesArisingFromFinancingActivities_349580da-da7b-4521-aefd-89513f8bc6e6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseThroughAmortizationCostRemeasurementLiabilitiesArisingFromFinancingActivities_d5ce1524-7c50-4146-b767-353427d5dfcf" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseThroughAmortizationCostRemeasurementLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_abvx_IncreaseDecreaseThroughAmortizationCostRemeasurementLiabilitiesArisingFromFinancingActivities_d5ce1524-7c50-4146-b767-353427d5dfcf" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughChangesInFairValuesLiabilitiesArisingFromFinancingActivities_41f36a07-4647-42d4-8054-d87ea063625d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughChangesInFairValuesLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughChangesInFairValuesLiabilitiesArisingFromFinancingActivities_41f36a07-4647-42d4-8054-d87ea063625d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseThroughSubsidiesLiabilitiesArisingFromFinancingActivities_652a1c84-6123-4462-98d4-9452c40662c5" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseThroughSubsidiesLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_abvx_IncreaseDecreaseThroughSubsidiesLiabilitiesArisingFromFinancingActivities_652a1c84-6123-4462-98d4-9452c40662c5" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseThroughConversionIntoSharesLiabilitiesArisingFromFinancingActivities_019c5738-0ffd-7187-af60-eca22b6709d2" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseThroughConversionIntoSharesLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_abvx_IncreaseDecreaseThroughConversionIntoSharesLiabilitiesArisingFromFinancingActivities_019c5738-0ffd-7187-af60-eca22b6709d2" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseThroughNewLeasesLiabilitiesArisingFromFinancingActivities_703b5c5e-be92-4805-bef4-2d232d095e58" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseThroughNewLeasesLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_ifrs-full_IncreaseThroughNewLeasesLiabilitiesArisingFromFinancingActivities_703b5c5e-be92-4805-bef4-2d232d095e58" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_IncreaseDecreaseThroughEffectOfChangesInForeignExchangeRatesLiabilitiesArisingFromFinancingActivities_b027fe05-2a2c-4657-b2bc-38fedd5840a0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughEffectOfChangesInForeignExchangeRatesLiabilitiesArisingFromFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems_75f23386-f6a4-40c2-896d-b4fed2d770cb" xlink:to="loc_ifrs-full_IncreaseDecreaseThroughEffectOfChangesInForeignExchangeRatesLiabilitiesArisingFromFinancingActivities_b027fe05-2a2c-4657-b2bc-38fedd5840a0" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LiabilitiesArisingFromFinancingActivities_c2bd0a5e-33c1-4cc9-8022-15b45bc34a83" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LiabilitiesArisingFromFinancingActivities"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesChangeinfinancialliabilitiesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesChangeinfinancialliabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesChangeinfinancialliabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_1991fa2a-be1c-4870-9876-5d351d3a7ec1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_e8f93a72-6a5d-45d9-95e0-0c82001df9bc" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_1991fa2a-be1c-4870-9876-5d351d3a7ec1" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_e8f93a72-6a5d-45d9-95e0-0c82001df9bc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_3b57197d-14b5-47b2-aa7b-479fa7e361f8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_e8f93a72-6a5d-45d9-95e0-0c82001df9bc" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_3b57197d-14b5-47b2-aa7b-479fa7e361f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_3b57197d-14b5-47b2-aa7b-479fa7e361f8_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_3b57197d-14b5-47b2-aa7b-479fa7e361f8" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_3b57197d-14b5-47b2-aa7b-479fa7e361f8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_c73c5a1e-8035-4a0c-ae6b-1ae46fa059dc" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_3b57197d-14b5-47b2-aa7b-479fa7e361f8" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_c73c5a1e-8035-4a0c-ae6b-1ae46fa059dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheAMember_bdef2de1-96d9-4070-90b5-b55be137a853" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_c73c5a1e-8035-4a0c-ae6b-1ae46fa059dc" xlink:to="loc_abvx_KreosClaretFinancingTrancheAMember_bdef2de1-96d9-4070-90b5-b55be137a853" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingSeniorSecuredNonConvertibleLoansMember_b7d5eba2-5c57-4d0c-9552-bd86dfbae26a" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingSeniorSecuredNonConvertibleLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_c73c5a1e-8035-4a0c-ae6b-1ae46fa059dc" xlink:to="loc_abvx_KreosClaretFinancingSeniorSecuredNonConvertibleLoansMember_b7d5eba2-5c57-4d0c-9552-bd86dfbae26a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_HeightsConvertibleNotesMember_ab8dcd51-05bc-4c53-8989-365c4304afde" xlink:href="abvx-20251231.xsd#abvx_HeightsConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_c73c5a1e-8035-4a0c-ae6b-1ae46fa059dc" xlink:to="loc_abvx_HeightsConvertibleNotesMember_ab8dcd51-05bc-4c53-8989-365c4304afde" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OCEANEMember_e196ca6b-d192-43eb-983e-3a6126027d7d" xlink:href="abvx-20251231.xsd#abvx_OCEANEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_c73c5a1e-8035-4a0c-ae6b-1ae46fa059dc" xlink:to="loc_abvx_OCEANEMember_e196ca6b-d192-43eb-983e-3a6126027d7d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheBMember_ea5144cb-2889-407b-a1ef-e365ab344db2" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_c73c5a1e-8035-4a0c-ae6b-1ae46fa059dc" xlink:to="loc_abvx_KreosClaretFinancingTrancheBMember_ea5144cb-2889-407b-a1ef-e365ab344db2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheCMember_ddba5ac9-d2bb-4e9a-ba4c-3b2c3ee40b70" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_c73c5a1e-8035-4a0c-ae6b-1ae46fa059dc" xlink:to="loc_abvx_KreosClaretFinancingTrancheCMember_ddba5ac9-d2bb-4e9a-ba4c-3b2c3ee40b70" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheABMember_6a33c444-7471-4690-a2b6-0310b9093661" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheABMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_c73c5a1e-8035-4a0c-ae6b-1ae46fa059dc" xlink:to="loc_abvx_KreosClaretFinancingTrancheABMember_6a33c444-7471-4690-a2b6-0310b9093661" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_8eca8f20-3b00-4783-b0a8-c0fa8b3e4a8b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_e8f93a72-6a5d-45d9-95e0-0c82001df9bc" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_8eca8f20-3b00-4783-b0a8-c0fa8b3e4a8b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_8eca8f20-3b00-4783-b0a8-c0fa8b3e4a8b_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_8eca8f20-3b00-4783-b0a8-c0fa8b3e4a8b" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_8eca8f20-3b00-4783-b0a8-c0fa8b3e4a8b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_9ce61c2e-d6dd-4fd6-bdf7-2b6718d3c28c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_8eca8f20-3b00-4783-b0a8-c0fa8b3e4a8b" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_9ce61c2e-d6dd-4fd6-bdf7-2b6718d3c28c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OceaneConversionOptionMember_4afaca7c-0471-4245-b697-abad4dcfa032" xlink:href="abvx-20251231.xsd#abvx_OceaneConversionOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_9ce61c2e-d6dd-4fd6-bdf7-2b6718d3c28c" xlink:to="loc_abvx_OceaneConversionOptionMember_4afaca7c-0471-4245-b697-abad4dcfa032" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PaymentsForDebtIssueCosts_00e5c24e-09f6-4add-859e-19985cfd53c2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PaymentsForDebtIssueCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_1991fa2a-be1c-4870-9876-5d351d3a7ec1" xlink:to="loc_ifrs-full_PaymentsForDebtIssueCosts_00e5c24e-09f6-4add-859e-19985cfd53c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NetProceedsFromConvertibleLoansNotes_c514cc74-8df9-4898-91f3-23e4908458cb" xlink:href="abvx-20251231.xsd#abvx_NetProceedsFromConvertibleLoansNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_1991fa2a-be1c-4870-9876-5d351d3a7ec1" xlink:to="loc_abvx_NetProceedsFromConvertibleLoansNotes_c514cc74-8df9-4898-91f3-23e4908458cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RepurchaseOfDerivativeInstruments_bfeced63-29c5-4619-80ac-a9180e07c1a9" xlink:href="abvx-20251231.xsd#abvx_RepurchaseOfDerivativeInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_1991fa2a-be1c-4870-9876-5d351d3a7ec1" xlink:to="loc_abvx_RepurchaseOfDerivativeInstruments_bfeced63-29c5-4619-80ac-a9180e07c1a9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RepaymentsOfConvertibleLoansNotes_5c40627c-eefa-4d99-a428-2ddf16c6a979" xlink:href="abvx-20251231.xsd#abvx_RepaymentsOfConvertibleLoansNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_1991fa2a-be1c-4870-9876-5d351d3a7ec1" xlink:to="loc_abvx_RepaymentsOfConvertibleLoansNotes_5c40627c-eefa-4d99-a428-2ddf16c6a979" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_GrossProceedsFromNonConvertibleLoansNotes_bbc3aa11-7581-4ed8-bf6e-1c81609ffb86" xlink:href="abvx-20251231.xsd#abvx_GrossProceedsFromNonConvertibleLoansNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_1991fa2a-be1c-4870-9876-5d351d3a7ec1" xlink:to="loc_abvx_GrossProceedsFromNonConvertibleLoansNotes_bbc3aa11-7581-4ed8-bf6e-1c81609ffb86" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsDiscountRate_019c5742-3d2a-70df-9dd5-08d040c2001b" xlink:href="abvx-20251231.xsd#abvx_BorrowingsDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_1991fa2a-be1c-4870-9876-5d351d3a7ec1" xlink:to="loc_abvx_BorrowingsDiscountRate_019c5742-3d2a-70df-9dd5-08d040c2001b" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesDisclosureofchangesinderivativeinstrumentsDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesDisclosureofchangesinderivativeinstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesDisclosureofchangesinderivativeinstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfFinancialInstrumentsLineItems_7afa4347-ce99-4133-8623-b24af27cbadd" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfFinancialInstrumentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfFinancialInstrumentsTable_e4c41bb0-a1d8-4fdd-ad1d-1b7f8ce1a4ff" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfFinancialInstrumentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfFinancialInstrumentsLineItems_7afa4347-ce99-4133-8623-b24af27cbadd" xlink:to="loc_ifrs-full_DisclosureOfFinancialInstrumentsTable_e4c41bb0-a1d8-4fdd-ad1d-1b7f8ce1a4ff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_1c56de6b-1a1a-4efa-9fb4-aae7eec8524d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfFinancialInstrumentsTable_e4c41bb0-a1d8-4fdd-ad1d-1b7f8ce1a4ff" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_1c56de6b-1a1a-4efa-9fb4-aae7eec8524d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_1c56de6b-1a1a-4efa-9fb4-aae7eec8524d_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_1c56de6b-1a1a-4efa-9fb4-aae7eec8524d" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_1c56de6b-1a1a-4efa-9fb4-aae7eec8524d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_b3c58368-7fe8-4cdb-9ee4-d272bd430e44" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_1c56de6b-1a1a-4efa-9fb4-aae7eec8524d" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_b3c58368-7fe8-4cdb-9ee4-d272bd430e44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosABSAMember_566ace77-5fb6-4623-b504-306f6c00db52" xlink:href="abvx-20251231.xsd#abvx_KreosABSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_b3c58368-7fe8-4cdb-9ee4-d272bd430e44" xlink:to="loc_abvx_KreosABSAMember_566ace77-5fb6-4623-b504-306f6c00db52" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosBBSAMember_4d7649f3-cd43-4f8c-9fa1-df10e9f9491e" xlink:href="abvx-20251231.xsd#abvx_KreosBBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_b3c58368-7fe8-4cdb-9ee4-d272bd430e44" xlink:to="loc_abvx_KreosBBSAMember_4d7649f3-cd43-4f8c-9fa1-df10e9f9491e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OceaneConversionOptionMember_b9b6fa8d-3cb8-4fef-9ea5-147e29cdd19e" xlink:href="abvx-20251231.xsd#abvx_OceaneConversionOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_b3c58368-7fe8-4cdb-9ee4-d272bd430e44" xlink:to="loc_abvx_OceaneConversionOptionMember_b9b6fa8d-3cb8-4fef-9ea5-147e29cdd19e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheAMember_1d558002-759d-4da6-9586-365b5b154f35" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_b3c58368-7fe8-4cdb-9ee4-d272bd430e44" xlink:to="loc_abvx_KreosClaretFinancingTrancheAMember_1d558002-759d-4da6-9586-365b5b154f35" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretMinimumReturnIndemnificationsMember_bbf812be-bbdd-40ee-bd8b-ca195c98c497" xlink:href="abvx-20251231.xsd#abvx_KreosClaretMinimumReturnIndemnificationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_b3c58368-7fe8-4cdb-9ee4-d272bd430e44" xlink:to="loc_abvx_KreosClaretMinimumReturnIndemnificationsMember_bbf812be-bbdd-40ee-bd8b-ca195c98c497" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DerivativeFinancialLiabilities_8d6b56ff-debc-46ee-b1be-b3cad6903a33" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DerivativeFinancialLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfFinancialInstrumentsLineItems_7afa4347-ce99-4133-8623-b24af27cbadd" xlink:to="loc_ifrs-full_DerivativeFinancialLiabilities_8d6b56ff-debc-46ee-b1be-b3cad6903a33" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IssuanceOfDerivativeInstruments_6cb447ec-a701-4b75-9148-e2c76e919001" xlink:href="abvx-20251231.xsd#abvx_IssuanceOfDerivativeInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfFinancialInstrumentsLineItems_7afa4347-ce99-4133-8623-b24af27cbadd" xlink:to="loc_abvx_IssuanceOfDerivativeInstruments_6cb447ec-a701-4b75-9148-e2c76e919001" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LossesOnChangeInFairValueOfDerivatives_4bceff72-93eb-40cd-beb7-68f0fdb7eb8b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LossesOnChangeInFairValueOfDerivatives"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfFinancialInstrumentsLineItems_7afa4347-ce99-4133-8623-b24af27cbadd" xlink:to="loc_ifrs-full_LossesOnChangeInFairValueOfDerivatives_4bceff72-93eb-40cd-beb7-68f0fdb7eb8b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GainsOnChangeInFairValueOfDerivatives_8b5f7ce6-8089-4e2f-bc66-aa94235b0dd3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GainsOnChangeInFairValueOfDerivatives"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfFinancialInstrumentsLineItems_7afa4347-ce99-4133-8623-b24af27cbadd" xlink:to="loc_ifrs-full_GainsOnChangeInFairValueOfDerivatives_8b5f7ce6-8089-4e2f-bc66-aa94235b0dd3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RepurchaseOfDerivativeInstruments_1362e66b-da37-4c33-9759-2652a43cc95d" xlink:href="abvx-20251231.xsd#abvx_RepurchaseOfDerivativeInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfFinancialInstrumentsLineItems_7afa4347-ce99-4133-8623-b24af27cbadd" xlink:to="loc_abvx_RepurchaseOfDerivativeInstruments_1362e66b-da37-4c33-9759-2652a43cc95d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExerciseOfDerivativeInstruments_56ec67d3-a9f4-4554-a3ac-ed163fa70994" xlink:href="abvx-20251231.xsd#abvx_ExerciseOfDerivativeInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfFinancialInstrumentsLineItems_7afa4347-ce99-4133-8623-b24af27cbadd" xlink:to="loc_abvx_ExerciseOfDerivativeInstruments_56ec67d3-a9f4-4554-a3ac-ed163fa70994" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DerivativeFinancialLiabilities_5ae8dc8d-e4ed-4fa0-b27b-bc490bb5de42" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DerivativeFinancialLiabilities"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesDisclosureofremainingcontractualmaturitiesoffinancialliabilitiesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesDisclosureofremainingcontractualmaturitiesoffinancialliabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesDisclosureofremainingcontractualmaturitiesoffinancialliabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesTable_78c0728d-f42e-412b-a2bd-f6711359ebf2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesTable_78c0728d-f42e-412b-a2bd-f6711359ebf2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_ea3aec78-05b5-4326-bf18-ac5f6556da84" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesTable_78c0728d-f42e-412b-a2bd-f6711359ebf2" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_ea3aec78-05b5-4326-bf18-ac5f6556da84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_ea3aec78-05b5-4326-bf18-ac5f6556da84_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_ea3aec78-05b5-4326-bf18-ac5f6556da84" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_ea3aec78-05b5-4326-bf18-ac5f6556da84_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_33e69911-32d6-4c73-b5fe-afd0aee5d5d8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_ea3aec78-05b5-4326-bf18-ac5f6556da84" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_33e69911-32d6-4c73-b5fe-afd0aee5d5d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_HeightsConvertibleNotesMember_daf64d0d-24d6-4715-afe6-fb8ca41e81c6" xlink:href="abvx-20251231.xsd#abvx_HeightsConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_33e69911-32d6-4c73-b5fe-afd0aee5d5d8" xlink:to="loc_abvx_HeightsConvertibleNotesMember_daf64d0d-24d6-4715-afe6-fb8ca41e81c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingTrancheAMember_7a522bae-aed3-4d89-a688-04d92aaea1a9" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingTrancheAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_33e69911-32d6-4c73-b5fe-afd0aee5d5d8" xlink:to="loc_abvx_KreosClaretFinancingTrancheAMember_7a522bae-aed3-4d89-a688-04d92aaea1a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretBondLoansMember_01e3ef08-07b5-446d-a0a1-d9ab70126131" xlink:href="abvx-20251231.xsd#abvx_KreosClaretBondLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_33e69911-32d6-4c73-b5fe-afd0aee5d5d8" xlink:to="loc_abvx_KreosClaretBondLoansMember_01e3ef08-07b5-446d-a0a1-d9ab70126131" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PretGarantiParLEtatPGEMember_4e01771a-2520-4921-a2b8-531749c18041" xlink:href="abvx-20251231.xsd#abvx_PretGarantiParLEtatPGEMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_33e69911-32d6-4c73-b5fe-afd0aee5d5d8" xlink:to="loc_abvx_PretGarantiParLEtatPGEMember_4e01771a-2520-4921-a2b8-531749c18041" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_MaturityAxis_af598c98-c654-492d-81be-aa3ce82e2313" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesTable_78c0728d-f42e-412b-a2bd-f6711359ebf2" xlink:to="loc_ifrs-full_MaturityAxis_af598c98-c654-492d-81be-aa3ce82e2313" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_MaturityDomain_af598c98-c654-492d-81be-aa3ce82e2313_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_MaturityAxis_af598c98-c654-492d-81be-aa3ce82e2313" xlink:to="loc_ifrs-full_MaturityDomain_af598c98-c654-492d-81be-aa3ce82e2313_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_MaturityDomain_2cb635f9-1f42-4f48-baae-2ffbabf23ecd" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_MaturityAxis_af598c98-c654-492d-81be-aa3ce82e2313" xlink:to="loc_ifrs-full_MaturityDomain_2cb635f9-1f42-4f48-baae-2ffbabf23ecd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NotLaterThanOneYearMember_6cae0916-883c-4d54-837e-033031636171" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NotLaterThanOneYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_MaturityDomain_2cb635f9-1f42-4f48-baae-2ffbabf23ecd" xlink:to="loc_ifrs-full_NotLaterThanOneYearMember_6cae0916-883c-4d54-837e-033031636171" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember_6537d6e5-99c3-4248-8abf-3743bc74a6b8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_MaturityDomain_2cb635f9-1f42-4f48-baae-2ffbabf23ecd" xlink:to="loc_ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember_6537d6e5-99c3-4248-8abf-3743bc74a6b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LaterThanTwoYearsAndNotLaterThanFiveYearsMember_82d5900f-9af5-4847-a885-8bf62529b823" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanTwoYearsAndNotLaterThanFiveYearsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_MaturityDomain_2cb635f9-1f42-4f48-baae-2ffbabf23ecd" xlink:to="loc_ifrs-full_LaterThanTwoYearsAndNotLaterThanFiveYearsMember_82d5900f-9af5-4847-a885-8bf62529b823" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LaterThanFiveYearsMember_be58fe9a-951f-4bb0-beff-b53cc2d0a77b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanFiveYearsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_MaturityDomain_2cb635f9-1f42-4f48-baae-2ffbabf23ecd" xlink:to="loc_ifrs-full_LaterThanFiveYearsMember_be58fe9a-951f-4bb0-beff-b53cc2d0a77b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConvertibleLoansNotes_fa315cb3-6f4a-4822-9cb1-7ccd0db304db" xlink:href="abvx-20251231.xsd#abvx_ConvertibleLoansNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_abvx_ConvertibleLoansNotes_fa315cb3-6f4a-4822-9cb1-7ccd0db304db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConvertibleLoansNotesUndiscountedCashFlows_61207533-2845-4a39-9be6-c6197f7b103e" xlink:href="abvx-20251231.xsd#abvx_ConvertibleLoansNotesUndiscountedCashFlows"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_abvx_ConvertibleLoansNotesUndiscountedCashFlows_61207533-2845-4a39-9be6-c6197f7b103e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_Borrowings_46d583cd-28a0-4e31-ba44-3e79e560b86d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Borrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_ifrs-full_Borrowings_46d583cd-28a0-4e31-ba44-3e79e560b86d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BankBorrowingsUndiscountedCashFlows_f629d02e-96bf-4abc-8c5c-62a31ead7e30" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BankBorrowingsUndiscountedCashFlows"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_ifrs-full_BankBorrowingsUndiscountedCashFlows_f629d02e-96bf-4abc-8c5c-62a31ead7e30" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConditionalAdvances_f99e1dee-1ac3-48bd-9574-adf1bb7beb71" xlink:href="abvx-20251231.xsd#abvx_ConditionalAdvances"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_abvx_ConditionalAdvances_f99e1dee-1ac3-48bd-9574-adf1bb7beb71" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ConditionalAdvancesUndiscountedCashFlows_4a11b72c-4a07-4a2a-a205-9e195aa996ff" xlink:href="abvx-20251231.xsd#abvx_ConditionalAdvancesUndiscountedCashFlows"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_abvx_ConditionalAdvancesUndiscountedCashFlows_4a11b72c-4a07-4a2a-a205-9e195aa996ff" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NonCurrentRoyaltyCertificates_4a1c6903-f5af-45bf-9f4e-c95dab965f67" xlink:href="abvx-20251231.xsd#abvx_NonCurrentRoyaltyCertificates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_abvx_NonCurrentRoyaltyCertificates_4a1c6903-f5af-45bf-9f4e-c95dab965f67" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RoyaltyCertificatesUndiscountedCashFlows_2258445e-c758-4575-ace5-880f2c9c3a0a" xlink:href="abvx-20251231.xsd#abvx_RoyaltyCertificatesUndiscountedCashFlows"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_abvx_RoyaltyCertificatesUndiscountedCashFlows_2258445e-c758-4575-ace5-880f2c9c3a0a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LeaseLiabilities_dc7fa830-86a7-4f99-beba-9f4f91abd249" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LeaseLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_ifrs-full_LeaseLiabilities_dc7fa830-86a7-4f99-beba-9f4f91abd249" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GrossLeaseLiabilities_5fb4362d-09e3-4c23-a3f5-b1aab072f7b2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GrossLeaseLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_ifrs-full_GrossLeaseLiabilities_5fb4362d-09e3-4c23-a3f5-b1aab072f7b2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DerivativeFinancialLiabilities_6a855fd7-7aaf-4b48-a80d-44e43e89638a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DerivativeFinancialLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_ifrs-full_DerivativeFinancialLiabilities_6a855fd7-7aaf-4b48-a80d-44e43e89638a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DerivativeFinancialLiabilitiesUndiscountedCashFlows_877fd5c3-7060-4e96-bda2-979d672c239f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DerivativeFinancialLiabilitiesUndiscountedCashFlows"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_ifrs-full_DerivativeFinancialLiabilitiesUndiscountedCashFlows_877fd5c3-7060-4e96-bda2-979d672c239f" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_FinancialLiabilities_ff47ff04-ec85-4b62-8600-cf904663e180" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FinancialLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_ifrs-full_FinancialLiabilities_ff47ff04-ec85-4b62-8600-cf904663e180" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_FinancialLiabilitiesUndiscountedCashFlows_09f0839f-90d6-4cc4-9c2d-6252144c91cb" xlink:href="abvx-20251231.xsd#abvx_FinancialLiabilitiesUndiscountedCashFlows"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_61d0bb6e-49e7-4306-b424-edce15fba592" xlink:to="loc_abvx_FinancialLiabilitiesUndiscountedCashFlows_09f0839f-90d6-4cc4-9c2d-6252144c91cb" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialliabilitiesBreakdownoffinancialliabilitiesbymaturityDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialliabilitiesBreakdownoffinancialliabilitiesbymaturityDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialliabilitiesBreakdownoffinancialliabilitiesbymaturityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_7c290df7-624d-45a2-af97-1e900ae3601a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_69933053-a9a4-4d0c-b6f7-e6d69c3f8541" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_7c290df7-624d-45a2-af97-1e900ae3601a" xlink:to="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_69933053-a9a4-4d0c-b6f7-e6d69c3f8541" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_980f766a-2fcd-4c79-a127-573f62590fd1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsTable_69933053-a9a4-4d0c-b6f7-e6d69c3f8541" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_980f766a-2fcd-4c79-a127-573f62590fd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_980f766a-2fcd-4c79-a127-573f62590fd1_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_980f766a-2fcd-4c79-a127-573f62590fd1" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_980f766a-2fcd-4c79-a127-573f62590fd1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_dab8e3f9-642c-4545-9372-fb9b3315ddb7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_980f766a-2fcd-4c79-a127-573f62590fd1" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_dab8e3f9-642c-4545-9372-fb9b3315ddb7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RoyaltyCertificatesMember_28fe38d4-9104-468e-abaf-cd874d5fbd04" xlink:href="abvx-20251231.xsd#abvx_RoyaltyCertificatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_dab8e3f9-642c-4545-9372-fb9b3315ddb7" xlink:to="loc_abvx_RoyaltyCertificatesMember_28fe38d4-9104-468e-abaf-cd874d5fbd04" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RoyaltyCertificatePercentageOfFutureSales_00f49b25-2e5a-4acf-9f90-4473e61bd9b1" xlink:href="abvx-20251231.xsd#abvx_RoyaltyCertificatePercentageOfFutureSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_7c290df7-624d-45a2-af97-1e900ae3601a" xlink:to="loc_abvx_RoyaltyCertificatePercentageOfFutureSales_00f49b25-2e5a-4acf-9f90-4473e61bd9b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RoyaltyCertificateMaximumAmount_656392d4-65dd-421d-a8e0-f8ada648d47c" xlink:href="abvx-20251231.xsd#abvx_RoyaltyCertificateMaximumAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_7c290df7-624d-45a2-af97-1e900ae3601a" xlink:to="loc_abvx_RoyaltyCertificateMaximumAmount_656392d4-65dd-421d-a8e0-f8ada648d47c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RoyaltyCertificateExpirationPeriod_b293b72a-6f01-463c-b9f3-7fb7ecc249bc" xlink:href="abvx-20251231.xsd#abvx_RoyaltyCertificateExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDetailedInformationAboutBorrowingsLineItems_7c290df7-624d-45a2-af97-1e900ae3601a" xlink:to="loc_abvx_RoyaltyCertificateExpirationPeriod_b293b72a-6f01-463c-b9f3-7fb7ecc249bc" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/RetirementbenefitobligationsDisclosureofmainactuarialassumptionsusedtomeasuretheretirementbenefitobligationsDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#RetirementbenefitobligationsDisclosureofmainactuarialassumptionsusedtomeasuretheretirementbenefitobligationsDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/RetirementbenefitobligationsDisclosureofmainactuarialassumptionsusedtomeasuretheretirementbenefitobligationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_448a5ca1-db79-4f97-a27a-0bf0dea7c8c9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDefinedBenefitPlansLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDefinedBenefitPlansTable_aba9a28c-3fa5-48f4-a0bf-bf15343e09ee" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDefinedBenefitPlansTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_448a5ca1-db79-4f97-a27a-0bf0dea7c8c9" xlink:to="loc_ifrs-full_DisclosureOfDefinedBenefitPlansTable_aba9a28c-3fa5-48f4-a0bf-bf15343e09ee" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_501f46a2-d6d6-4aaf-a203-286b1aee64b9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansTable_aba9a28c-3fa5-48f4-a0bf-bf15343e09ee" xlink:to="loc_srt_TitleOfIndividualAxis_501f46a2-d6d6-4aaf-a203-286b1aee64b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_501f46a2-d6d6-4aaf-a203-286b1aee64b9_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_501f46a2-d6d6-4aaf-a203-286b1aee64b9" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_501f46a2-d6d6-4aaf-a203-286b1aee64b9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_1ef1e6c0-bb21-456e-9c31-43a13210feba" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_501f46a2-d6d6-4aaf-a203-286b1aee64b9" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_1ef1e6c0-bb21-456e-9c31-43a13210feba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ManagementMember_96284b31-0d04-4b44-b52d-6058279c61a3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ManagementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_1ef1e6c0-bb21-456e-9c31-43a13210feba" xlink:to="loc_srt_ManagementMember_96284b31-0d04-4b44-b52d-6058279c61a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherEmployeesMember_8dc302c4-0756-4d25-9510-3f3eb4a2abcf" xlink:href="abvx-20251231.xsd#abvx_OtherEmployeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_1ef1e6c0-bb21-456e-9c31-43a13210feba" xlink:to="loc_abvx_OtherEmployeesMember_8dc302c4-0756-4d25-9510-3f3eb4a2abcf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_1c5dbe2b-29b1-4067-b5af-262e3e1476d8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansTable_aba9a28c-3fa5-48f4-a0bf-bf15343e09ee" xlink:to="loc_srt_RangeAxis_1c5dbe2b-29b1-4067-b5af-262e3e1476d8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1c5dbe2b-29b1-4067-b5af-262e3e1476d8_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_1c5dbe2b-29b1-4067-b5af-262e3e1476d8" xlink:to="loc_srt_RangeMember_1c5dbe2b-29b1-4067-b5af-262e3e1476d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1e0b7bf8-5c7e-47ef-9719-4b889bc1073c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_1c5dbe2b-29b1-4067-b5af-262e3e1476d8" xlink:to="loc_srt_RangeMember_1e0b7bf8-5c7e-47ef-9719-4b889bc1073c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TopOfRangeMember_0fbfd571-11ae-4a45-901c-09aad3443838" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TopOfRangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1e0b7bf8-5c7e-47ef-9719-4b889bc1073c" xlink:to="loc_ifrs-full_TopOfRangeMember_0fbfd571-11ae-4a45-901c-09aad3443838" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BottomOfRangeMember_25ea520a-50a1-4104-8926-2f4f85c10ed8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BottomOfRangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1e0b7bf8-5c7e-47ef-9719-4b889bc1073c" xlink:to="loc_ifrs-full_BottomOfRangeMember_25ea520a-50a1-4104-8926-2f4f85c10ed8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ActuarialAssumptionOfRetirementAge2019_77ac4d3b-0b90-4a60-9167-3be35f153f04" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ActuarialAssumptionOfRetirementAge2019"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_448a5ca1-db79-4f97-a27a-0bf0dea7c8c9" xlink:to="loc_ifrs-full_ActuarialAssumptionOfRetirementAge2019_77ac4d3b-0b90-4a60-9167-3be35f153f04" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ActuarialAssumptionOfDiscountRates_ddd886f1-9db6-4155-a7dd-f428ff91d637" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ActuarialAssumptionOfDiscountRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_448a5ca1-db79-4f97-a27a-0bf0dea7c8c9" xlink:to="loc_ifrs-full_ActuarialAssumptionOfDiscountRates_ddd886f1-9db6-4155-a7dd-f428ff91d637" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ActuarialAssumptionOfExpectedRatesOfSalaryIncreases_86063ad2-6c0a-45a7-9120-8f8ee717bafd" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ActuarialAssumptionOfExpectedRatesOfSalaryIncreases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_448a5ca1-db79-4f97-a27a-0bf0dea7c8c9" xlink:to="loc_ifrs-full_ActuarialAssumptionOfExpectedRatesOfSalaryIncreases_86063ad2-6c0a-45a7-9120-8f8ee717bafd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ActuarialAssumptionOfExpectedRatesOfTurnover_1ca547d8-b47c-4909-85be-9fe4a9c9e98b" xlink:href="abvx-20251231.xsd#abvx_ActuarialAssumptionOfExpectedRatesOfTurnover"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_448a5ca1-db79-4f97-a27a-0bf0dea7c8c9" xlink:to="loc_abvx_ActuarialAssumptionOfExpectedRatesOfTurnover_1ca547d8-b47c-4909-85be-9fe4a9c9e98b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ActuarialAssumptionOfExpectedRatesOfTurnoverAverageExitRate_015444ef-74a1-4220-8dca-9fa2a70b13e3" xlink:href="abvx-20251231.xsd#abvx_ActuarialAssumptionOfExpectedRatesOfTurnoverAverageExitRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_448a5ca1-db79-4f97-a27a-0bf0dea7c8c9" xlink:to="loc_abvx_ActuarialAssumptionOfExpectedRatesOfTurnoverAverageExitRate_015444ef-74a1-4220-8dca-9fa2a70b13e3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ActuarialAssumptionOfEmployeeContributionRate_7afa45db-841e-4f8e-a0c9-2074ec1b8e28" xlink:href="abvx-20251231.xsd#abvx_ActuarialAssumptionOfEmployeeContributionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_448a5ca1-db79-4f97-a27a-0bf0dea7c8c9" xlink:to="loc_abvx_ActuarialAssumptionOfEmployeeContributionRate_7afa45db-841e-4f8e-a0c9-2074ec1b8e28" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/RetirementbenefitobligationsDisclosureofchangesinprojectedbenefitobligationDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#RetirementbenefitobligationsDisclosureofchangesinprojectedbenefitobligationDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/RetirementbenefitobligationsDisclosureofchangesinprojectedbenefitobligationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_c68624e3-f0c9-4545-ab15-b13051cc1aeb" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDefinedBenefitPlansLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfDefinedBenefitPlansTable_c6baee42-b9f3-4915-aca0-fa880a01cb59" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDefinedBenefitPlansTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_c68624e3-f0c9-4545-ab15-b13051cc1aeb" xlink:to="loc_ifrs-full_DisclosureOfDefinedBenefitPlansTable_c6baee42-b9f3-4915-aca0-fa880a01cb59" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NetDefinedBenefitLiabilityAssetAxis_c53aa916-97d8-47bb-8a7c-d31d1f02bee2" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NetDefinedBenefitLiabilityAssetAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansTable_c6baee42-b9f3-4915-aca0-fa880a01cb59" xlink:to="loc_ifrs-full_NetDefinedBenefitLiabilityAssetAxis_c53aa916-97d8-47bb-8a7c-d31d1f02bee2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NetDefinedBenefitLiabilityAssetDomain_c53aa916-97d8-47bb-8a7c-d31d1f02bee2_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NetDefinedBenefitLiabilityAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_NetDefinedBenefitLiabilityAssetAxis_c53aa916-97d8-47bb-8a7c-d31d1f02bee2" xlink:to="loc_ifrs-full_NetDefinedBenefitLiabilityAssetDomain_c53aa916-97d8-47bb-8a7c-d31d1f02bee2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_NetDefinedBenefitLiabilityAssetDomain_c9500674-0774-435e-ae96-2c38a8bc8f40" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NetDefinedBenefitLiabilityAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_NetDefinedBenefitLiabilityAssetAxis_c53aa916-97d8-47bb-8a7c-d31d1f02bee2" xlink:to="loc_ifrs-full_NetDefinedBenefitLiabilityAssetDomain_c9500674-0774-435e-ae96-2c38a8bc8f40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PresentValueOfDefinedBenefitObligationMember_91ec1a10-5e7b-478a-8ba0-4578d29ba950" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PresentValueOfDefinedBenefitObligationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_NetDefinedBenefitLiabilityAssetDomain_c9500674-0774-435e-ae96-2c38a8bc8f40" xlink:to="loc_ifrs-full_PresentValueOfDefinedBenefitObligationMember_91ec1a10-5e7b-478a-8ba0-4578d29ba950" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LiabilityAssetOfDefinedBenefitPlans_a7edb470-00f2-48c0-86b5-df461c113bc8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LiabilityAssetOfDefinedBenefitPlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_c68624e3-f0c9-4545-ab15-b13051cc1aeb" xlink:to="loc_ifrs-full_LiabilityAssetOfDefinedBenefitPlans_a7edb470-00f2-48c0-86b5-df461c113bc8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CurrentServiceCostNetDefinedBenefitLiabilityAsset_4e0286b3-22b9-4f7f-b84e-aa186fc0e4db" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CurrentServiceCostNetDefinedBenefitLiabilityAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_c68624e3-f0c9-4545-ab15-b13051cc1aeb" xlink:to="loc_ifrs-full_CurrentServiceCostNetDefinedBenefitLiabilityAsset_4e0286b3-22b9-4f7f-b84e-aa186fc0e4db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PastServiceCostNetDefinedBenefitLiabilityAsset_019c574f-b20b-71d4-9d35-26f20dc47f7a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PastServiceCostNetDefinedBenefitLiabilityAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_c68624e3-f0c9-4545-ab15-b13051cc1aeb" xlink:to="loc_ifrs-full_PastServiceCostNetDefinedBenefitLiabilityAsset_019c574f-b20b-71d4-9d35-26f20dc47f7a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_InterestExpenseIncomeNetDefinedBenefitLiabilityAsset_07a1dffe-7d45-42d5-a9af-473ce0d11b3d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_InterestExpenseIncomeNetDefinedBenefitLiabilityAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_c68624e3-f0c9-4545-ab15-b13051cc1aeb" xlink:to="loc_ifrs-full_InterestExpenseIncomeNetDefinedBenefitLiabilityAsset_07a1dffe-7d45-42d5-a9af-473ce0d11b3d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_PaymentsFromPlanNetDefinedBenefitLiabilityAsset_d4476b4b-7310-405e-a248-b530bd24ad7a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PaymentsFromPlanNetDefinedBenefitLiabilityAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_c68624e3-f0c9-4545-ab15-b13051cc1aeb" xlink:to="loc_ifrs-full_PaymentsFromPlanNetDefinedBenefitLiabilityAsset_d4476b4b-7310-405e-a248-b530bd24ad7a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GainLossOnRemeasurementOfNetDefinedBenefitLiabilityAsset_a2ffc485-43bf-41ca-952f-af87a3d013e9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GainLossOnRemeasurementOfNetDefinedBenefitLiabilityAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfDefinedBenefitPlansLineItems_c68624e3-f0c9-4545-ab15-b13051cc1aeb" xlink:to="loc_ifrs-full_GainLossOnRemeasurementOfNetDefinedBenefitLiabilityAsset_a2ffc485-43bf-41ca-952f-af87a3d013e9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LiabilityAssetOfDefinedBenefitPlans_f5560863-0c60-4f86-94d8-701ae2d667c6" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LiabilityAssetOfDefinedBenefitPlans"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/OtheroperatingincomeNarrativeDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#OtheroperatingincomeNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/OtheroperatingincomeNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfOperatingIncomeLineItems_6a0c878d-703a-4f1a-a96f-6d5a25197c25" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfOperatingIncomeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfOperatingIncomeTable_56f401eb-af87-4f50-af47-20ad9c7fc2c3" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfOperatingIncomeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_abvx_DisclosureOfOperatingIncomeLineItems_6a0c878d-703a-4f1a-a96f-6d5a25197c25" xlink:to="loc_abvx_DisclosureOfOperatingIncomeTable_56f401eb-af87-4f50-af47-20ad9c7fc2c3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CIRTaxYearAxis_d092d1c5-2054-4df4-88e7-ce84bda2ea84" xlink:href="abvx-20251231.xsd#abvx_CIRTaxYearAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfOperatingIncomeTable_56f401eb-af87-4f50-af47-20ad9c7fc2c3" xlink:to="loc_abvx_CIRTaxYearAxis_d092d1c5-2054-4df4-88e7-ce84bda2ea84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CIRTaxYearDomain_d092d1c5-2054-4df4-88e7-ce84bda2ea84_default" xlink:href="abvx-20251231.xsd#abvx_CIRTaxYearDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_CIRTaxYearAxis_d092d1c5-2054-4df4-88e7-ce84bda2ea84" xlink:to="loc_abvx_CIRTaxYearDomain_d092d1c5-2054-4df4-88e7-ce84bda2ea84_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CIRTaxYearDomain_af3ad0be-0b56-4461-9b92-0e300f1f613f" xlink:href="abvx-20251231.xsd#abvx_CIRTaxYearDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_CIRTaxYearAxis_d092d1c5-2054-4df4-88e7-ce84bda2ea84" xlink:to="loc_abvx_CIRTaxYearDomain_af3ad0be-0b56-4461-9b92-0e300f1f613f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_A2021TaxYearMember_019c57c7-c3d0-786c-94c7-1114b0062dca" xlink:href="abvx-20251231.xsd#abvx_A2021TaxYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_CIRTaxYearDomain_af3ad0be-0b56-4461-9b92-0e300f1f613f" xlink:to="loc_abvx_A2021TaxYearMember_019c57c7-c3d0-786c-94c7-1114b0062dca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_A2022TaxYearMember_93df0bc2-2ec9-4ffe-9001-e1c2969b230f" xlink:href="abvx-20251231.xsd#abvx_A2022TaxYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_CIRTaxYearDomain_af3ad0be-0b56-4461-9b92-0e300f1f613f" xlink:to="loc_abvx_A2022TaxYearMember_93df0bc2-2ec9-4ffe-9001-e1c2969b230f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_A2023TaxYearMember_ce3fbb32-0da5-41df-8a60-0cc00df080a9" xlink:href="abvx-20251231.xsd#abvx_A2023TaxYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_CIRTaxYearDomain_af3ad0be-0b56-4461-9b92-0e300f1f613f" xlink:to="loc_abvx_A2023TaxYearMember_ce3fbb32-0da5-41df-8a60-0cc00df080a9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_A2024TaxYearMember_019c5757-3845-71f1-9aec-29380bc8b04a" xlink:href="abvx-20251231.xsd#abvx_A2024TaxYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_CIRTaxYearDomain_af3ad0be-0b56-4461-9b92-0e300f1f613f" xlink:to="loc_abvx_A2024TaxYearMember_019c5757-3845-71f1-9aec-29380bc8b04a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_3ea93f68-e7c8-42b7-8726-2bc7c3d01b9f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfOperatingIncomeTable_56f401eb-af87-4f50-af47-20ad9c7fc2c3" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_3ea93f68-e7c8-42b7-8726-2bc7c3d01b9f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_3ea93f68-e7c8-42b7-8726-2bc7c3d01b9f_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_3ea93f68-e7c8-42b7-8726-2bc7c3d01b9f" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_3ea93f68-e7c8-42b7-8726-2bc7c3d01b9f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_fedc0c49-3215-404e-9fd4-b3cf4ee44644" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_3ea93f68-e7c8-42b7-8726-2bc7c3d01b9f" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_fedc0c49-3215-404e-9fd4-b3cf4ee44644" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RNPVIRConditionalAdvanceBPIMember_86f1976a-b7f4-4625-a63f-c234b3bb52e7" xlink:href="abvx-20251231.xsd#abvx_RNPVIRConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_fedc0c49-3215-404e-9fd4-b3cf4ee44644" xlink:to="loc_abvx_RNPVIRConditionalAdvanceBPIMember_86f1976a-b7f4-4625-a63f-c234b3bb52e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CARENAConditionalAdvanceBPIMember_c644d6eb-0924-44cf-81e8-31983ab6df4e" xlink:href="abvx-20251231.xsd#abvx_CARENAConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_fedc0c49-3215-404e-9fd4-b3cf4ee44644" xlink:to="loc_abvx_CARENAConditionalAdvanceBPIMember_c644d6eb-0924-44cf-81e8-31983ab6df4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncomeFromResearchTaxCredit_b9e38762-16bc-4f93-aa64-53aa7e2c4972" xlink:href="abvx-20251231.xsd#abvx_IncomeFromResearchTaxCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOperatingIncomeLineItems_6a0c878d-703a-4f1a-a96f-6d5a25197c25" xlink:to="loc_abvx_IncomeFromResearchTaxCredit_b9e38762-16bc-4f93-aa64-53aa7e2c4972" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RevenueFromGovernmentGrants_03c31e27-ef28-403e-b47e-99b6ebaeb707" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RevenueFromGovernmentGrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOperatingIncomeLineItems_6a0c878d-703a-4f1a-a96f-6d5a25197c25" xlink:to="loc_ifrs-full_RevenueFromGovernmentGrants_03c31e27-ef28-403e-b47e-99b6ebaeb707" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_MiscellaneousOtherOperatingIncome_019bffc0-2d78-748f-96ec-5054c2cd9d89" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MiscellaneousOtherOperatingIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOperatingIncomeLineItems_6a0c878d-703a-4f1a-a96f-6d5a25197c25" xlink:to="loc_ifrs-full_MiscellaneousOtherOperatingIncome_019bffc0-2d78-748f-96ec-5054c2cd9d89" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/OperatingexpensesDisclosureofsalesandmarketingexpensesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#OperatingexpensesDisclosureofsalesandmarketingexpensesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/OperatingexpensesDisclosureofsalesandmarketingexpensesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_d47287a5-cf04-4bc9-8d4a-39275498515f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable_e111342d-013e-4844-a178-daa2197c24ea" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_d47287a5-cf04-4bc9-8d4a-39275498515f" xlink:to="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable_e111342d-013e-4844-a178-daa2197c24ea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_4f16b5af-f063-4f2d-a194-14df8d4a6cfc" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable_e111342d-013e-4844-a178-daa2197c24ea" xlink:to="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_4f16b5af-f063-4f2d-a194-14df8d4a6cfc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_4f16b5af-f063-4f2d-a194-14df8d4a6cfc_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_4f16b5af-f063-4f2d-a194-14df8d4a6cfc" xlink:to="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_4f16b5af-f063-4f2d-a194-14df8d4a6cfc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_9531b110-6d5f-4ecb-ba58-f875b10d44fd" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_4f16b5af-f063-4f2d-a194-14df8d4a6cfc" xlink:to="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_9531b110-6d5f-4ecb-ba58-f875b10d44fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SalesAndMarketingExpenseMember_75edeee1-5f58-4fd0-a85a-bdb601c3229d" xlink:href="abvx-20251231.xsd#abvx_SalesAndMarketingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_9531b110-6d5f-4ecb-ba58-f875b10d44fd" xlink:to="loc_abvx_SalesAndMarketingExpenseMember_75edeee1-5f58-4fd0-a85a-bdb601c3229d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_EmployeeBenefitsExpense_ab5e663b-24cf-4bd9-8703-31dbf6268b8b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_EmployeeBenefitsExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_d47287a5-cf04-4bc9-8d4a-39275498515f" xlink:to="loc_ifrs-full_EmployeeBenefitsExpense_ab5e663b-24cf-4bd9-8703-31dbf6268b8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProfessionalFeesExpense_49e3bac6-7400-49f9-901b-e8bc8560611d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProfessionalFeesExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_d47287a5-cf04-4bc9-8d4a-39275498515f" xlink:to="loc_ifrs-full_ProfessionalFeesExpense_49e3bac6-7400-49f9-901b-e8bc8560611d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_MiscellaneousOtherOperatingExpense_670a5238-641c-4cc5-9436-54016aef2cfb" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MiscellaneousOtherOperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_d47287a5-cf04-4bc9-8d4a-39275498515f" xlink:to="loc_ifrs-full_MiscellaneousOtherOperatingExpense_670a5238-641c-4cc5-9436-54016aef2cfb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OperatingExpense_00b9cb9a-08b9-48d8-9e48-843059004191" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_d47287a5-cf04-4bc9-8d4a-39275498515f" xlink:to="loc_ifrs-full_OperatingExpense_00b9cb9a-08b9-48d8-9e48-843059004191" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/OperatingexpensesDisclosureofresearchanddevelopmentexpensesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#OperatingexpensesDisclosureofresearchanddevelopmentexpensesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/OperatingexpensesDisclosureofresearchanddevelopmentexpensesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_ebd76308-81a8-4890-a9a5-bb4c0da2b8a4" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable_dbb757cd-2a1a-402f-a41c-adf77445c2c6" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_ebd76308-81a8-4890-a9a5-bb4c0da2b8a4" xlink:to="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable_dbb757cd-2a1a-402f-a41c-adf77445c2c6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_9bdb8aea-2421-470c-91c9-54e0c163388e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable_dbb757cd-2a1a-402f-a41c-adf77445c2c6" xlink:to="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_9bdb8aea-2421-470c-91c9-54e0c163388e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_9bdb8aea-2421-470c-91c9-54e0c163388e_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_9bdb8aea-2421-470c-91c9-54e0c163388e" xlink:to="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_9bdb8aea-2421-470c-91c9-54e0c163388e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_7e494e66-8f52-4d81-aebf-b6a1f3d91264" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_9bdb8aea-2421-470c-91c9-54e0c163388e" xlink:to="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_7e494e66-8f52-4d81-aebf-b6a1f3d91264" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ResearchAndDevelopmentExpensesMember_4b42726e-4c5f-45ea-8f2e-f322303d054b" xlink:href="abvx-20251231.xsd#abvx_ResearchAndDevelopmentExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_7e494e66-8f52-4d81-aebf-b6a1f3d91264" xlink:to="loc_abvx_ResearchAndDevelopmentExpensesMember_4b42726e-4c5f-45ea-8f2e-f322303d054b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SubContractingStudiesAndResearchExpenses_fd69e967-b49c-4161-8420-76146b330684" xlink:href="abvx-20251231.xsd#abvx_SubContractingStudiesAndResearchExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_ebd76308-81a8-4890-a9a5-bb4c0da2b8a4" xlink:to="loc_abvx_SubContractingStudiesAndResearchExpenses_fd69e967-b49c-4161-8420-76146b330684" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_EmployeeBenefitsExpense_4fc9f15f-2910-4fe3-a3a6-95d65638429e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_EmployeeBenefitsExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_ebd76308-81a8-4890-a9a5-bb4c0da2b8a4" xlink:to="loc_ifrs-full_EmployeeBenefitsExpense_4fc9f15f-2910-4fe3-a3a6-95d65638429e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProfessionalFeesExpense_0ee7937b-bdc4-45b7-a980-3195ecd124a8" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProfessionalFeesExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_ebd76308-81a8-4890-a9a5-bb4c0da2b8a4" xlink:to="loc_ifrs-full_ProfessionalFeesExpense_0ee7937b-bdc4-45b7-a980-3195ecd124a8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IntellectualPropertyFees_1728d476-5f76-4529-a4ab-e1b0724560fc" xlink:href="abvx-20251231.xsd#abvx_IntellectualPropertyFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_ebd76308-81a8-4890-a9a5-bb4c0da2b8a4" xlink:to="loc_abvx_IntellectualPropertyFees_1728d476-5f76-4529-a4ab-e1b0724560fc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_MiscellaneousOtherOperatingExpense_15616933-d9db-40c4-ad78-9a8e8de310e3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MiscellaneousOtherOperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_ebd76308-81a8-4890-a9a5-bb4c0da2b8a4" xlink:to="loc_ifrs-full_MiscellaneousOtherOperatingExpense_15616933-d9db-40c4-ad78-9a8e8de310e3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OperatingExpense_b96692b8-f591-4329-8217-ecb641ae7bbc" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_ebd76308-81a8-4890-a9a5-bb4c0da2b8a4" xlink:to="loc_ifrs-full_OperatingExpense_b96692b8-f591-4329-8217-ecb641ae7bbc" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/OperatingexpensesNarrativeDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#OperatingexpensesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/OperatingexpensesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_5ff4f599-2f10-4b78-b031-a824a56c98d4" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable_77e3b522-ca3c-4180-8026-b656f35ce963" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_5ff4f599-2f10-4b78-b031-a824a56c98d4" xlink:to="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable_77e3b522-ca3c-4180-8026-b656f35ce963" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_8b608cc6-7531-49f1-8888-0b03b54577b3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable_77e3b522-ca3c-4180-8026-b656f35ce963" xlink:to="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_8b608cc6-7531-49f1-8888-0b03b54577b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_8b608cc6-7531-49f1-8888-0b03b54577b3_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_8b608cc6-7531-49f1-8888-0b03b54577b3" xlink:to="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_8b608cc6-7531-49f1-8888-0b03b54577b3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_9f8d028c-4e32-4b10-8589-ce1aa236b6da" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_8b608cc6-7531-49f1-8888-0b03b54577b3" xlink:to="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_9f8d028c-4e32-4b10-8589-ce1aa236b6da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ResearchAndDevelopmentExpensesMember_7411fda6-cede-4123-98cc-e1b4256d701c" xlink:href="abvx-20251231.xsd#abvx_ResearchAndDevelopmentExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_9f8d028c-4e32-4b10-8589-ce1aa236b6da" xlink:to="loc_abvx_ResearchAndDevelopmentExpensesMember_7411fda6-cede-4123-98cc-e1b4256d701c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_GeneralAndAdministrativeExpensesMember_019c57c8-2813-7d73-9d97-2b9a73ab9be8" xlink:href="abvx-20251231.xsd#abvx_GeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_9f8d028c-4e32-4b10-8589-ce1aa236b6da" xlink:to="loc_abvx_GeneralAndAdministrativeExpensesMember_019c57c8-2813-7d73-9d97-2b9a73ab9be8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInUlcerativeColitisExpenses_128d9b10-b818-4c7d-afd7-f1b0040e0348" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInUlcerativeColitisExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_5ff4f599-2f10-4b78-b031-a824a56c98d4" xlink:to="loc_abvx_IncreaseDecreaseInUlcerativeColitisExpenses_128d9b10-b818-4c7d-afd7-f1b0040e0348" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInCrohnsDiseaseResearchExpenses_f3da0fc1-a68d-4e75-85fe-46cc481c91b0" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInCrohnsDiseaseResearchExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_5ff4f599-2f10-4b78-b031-a824a56c98d4" xlink:to="loc_abvx_IncreaseDecreaseInCrohnsDiseaseResearchExpenses_f3da0fc1-a68d-4e75-85fe-46cc481c91b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInTransversalActivities_2caf2588-4072-4c77-a905-1a77bd76517f" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInTransversalActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_5ff4f599-2f10-4b78-b031-a824a56c98d4" xlink:to="loc_abvx_IncreaseDecreaseInTransversalActivities_2caf2588-4072-4c77-a905-1a77bd76517f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInTransversalActivitiesCombinationTherapy_019cd7fb-00dd-7629-8b23-1c7eeb03b411" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInTransversalActivitiesCombinationTherapy"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_5ff4f599-2f10-4b78-b031-a824a56c98d4" xlink:to="loc_abvx_IncreaseDecreaseInTransversalActivitiesCombinationTherapy_019cd7fb-00dd-7629-8b23-1c7eeb03b411" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_IncreaseDecreaseInEmployerTaxAndSocialContributions_019c5760-de97-7279-9745-69b6019c74e4" xlink:href="abvx-20251231.xsd#abvx_IncreaseDecreaseInEmployerTaxAndSocialContributions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_5ff4f599-2f10-4b78-b031-a824a56c98d4" xlink:to="loc_abvx_IncreaseDecreaseInEmployerTaxAndSocialContributions_019c5760-de97-7279-9745-69b6019c74e4" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/OperatingexpensesDisclosureofgeneralandadministrativeexpensesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#OperatingexpensesDisclosureofgeneralandadministrativeexpensesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/OperatingexpensesDisclosureofgeneralandadministrativeexpensesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_359e8ed5-8025-433a-9192-4365c1486c4c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable_8f36584e-cdc2-4ce2-a60c-d495cb54271b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_359e8ed5-8025-433a-9192-4365c1486c4c" xlink:to="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable_8f36584e-cdc2-4ce2-a60c-d495cb54271b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_b4f5791e-7bf4-4f5b-8bc8-b6f627e90fa7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionTable_8f36584e-cdc2-4ce2-a60c-d495cb54271b" xlink:to="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_b4f5791e-7bf4-4f5b-8bc8-b6f627e90fa7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_b4f5791e-7bf4-4f5b-8bc8-b6f627e90fa7_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_b4f5791e-7bf4-4f5b-8bc8-b6f627e90fa7" xlink:to="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_b4f5791e-7bf4-4f5b-8bc8-b6f627e90fa7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_f09a4a39-0b42-4999-9bd4-12a46f053748" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis_b4f5791e-7bf4-4f5b-8bc8-b6f627e90fa7" xlink:to="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_f09a4a39-0b42-4999-9bd4-12a46f053748" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_GeneralAndAdministrativeExpensesMember_feb1d90b-a3c4-49ae-828d-028e8090aaf7" xlink:href="abvx-20251231.xsd#abvx_GeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_AttributionOfExpensesByNatureToTheirFunctionDomain_f09a4a39-0b42-4999-9bd4-12a46f053748" xlink:to="loc_abvx_GeneralAndAdministrativeExpensesMember_feb1d90b-a3c4-49ae-828d-028e8090aaf7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_EmployeeBenefitsExpense_a7d95776-9139-4222-a491-0c5d9779b0f6" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_EmployeeBenefitsExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_359e8ed5-8025-433a-9192-4365c1486c4c" xlink:to="loc_ifrs-full_EmployeeBenefitsExpense_a7d95776-9139-4222-a491-0c5d9779b0f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProfessionalFeesExpense_ebb36c3c-e025-4bbd-819d-b0c8b8fddb0a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProfessionalFeesExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_359e8ed5-8025-433a-9192-4365c1486c4c" xlink:to="loc_ifrs-full_ProfessionalFeesExpense_ebb36c3c-e025-4bbd-819d-b0c8b8fddb0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_MiscellaneousOtherOperatingExpense_e99eca0f-c97c-4c70-8e40-7c3ea8f6d611" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MiscellaneousOtherOperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_359e8ed5-8025-433a-9192-4365c1486c4c" xlink:to="loc_ifrs-full_MiscellaneousOtherOperatingExpense_e99eca0f-c97c-4c70-8e40-7c3ea8f6d611" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OperatingExpense_0bd5f6f2-56d1-471b-9738-652c19b30a0f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfAttributionOfExpensesByNatureToTheirFunctionLineItems_359e8ed5-8025-433a-9192-4365c1486c4c" xlink:to="loc_ifrs-full_OperatingExpense_0bd5f6f2-56d1-471b-9738-652c19b30a0f" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/EmployeesDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#EmployeesDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/EmployeesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfEmployeeWorkforceLineItems_44f1647b-9cbb-4213-b2b4-b8a3447bc51b" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfEmployeeWorkforceLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfEmployeeWorkforceTable_b0f5829c-995d-4b09-b256-9f247c94176e" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfEmployeeWorkforceTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_abvx_DisclosureOfEmployeeWorkforceLineItems_44f1647b-9cbb-4213-b2b4-b8a3447bc51b" xlink:to="loc_abvx_DisclosureOfEmployeeWorkforceTable_b0f5829c-995d-4b09-b256-9f247c94176e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GeographicalAreasAxis_577fa728-3dfc-488b-a7ff-5a5ab3f35d2e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GeographicalAreasAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfEmployeeWorkforceTable_b0f5829c-995d-4b09-b256-9f247c94176e" xlink:to="loc_ifrs-full_GeographicalAreasAxis_577fa728-3dfc-488b-a7ff-5a5ab3f35d2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GeographicalAreasDomain_577fa728-3dfc-488b-a7ff-5a5ab3f35d2e_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GeographicalAreasDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_GeographicalAreasAxis_577fa728-3dfc-488b-a7ff-5a5ab3f35d2e" xlink:to="loc_ifrs-full_GeographicalAreasDomain_577fa728-3dfc-488b-a7ff-5a5ab3f35d2e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GeographicalAreasDomain_ba565072-5408-4efc-9aa3-62b1c7644aea" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GeographicalAreasDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_GeographicalAreasAxis_577fa728-3dfc-488b-a7ff-5a5ab3f35d2e" xlink:to="loc_ifrs-full_GeographicalAreasDomain_ba565072-5408-4efc-9aa3-62b1c7644aea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_FR_ab53a958-b7cc-4ea1-8d00-470171dec908" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_FR"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_GeographicalAreasDomain_ba565072-5408-4efc-9aa3-62b1c7644aea" xlink:to="loc_country_FR_ab53a958-b7cc-4ea1-8d00-470171dec908" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_99c01d91-dd40-499b-a9be-8b7259c957a1" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_GeographicalAreasDomain_ba565072-5408-4efc-9aa3-62b1c7644aea" xlink:to="loc_country_US_99c01d91-dd40-499b-a9be-8b7259c957a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_AverageNumberOfEmployees_27ee2524-90a1-4a9b-8c84-4a13365f7409" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AverageNumberOfEmployees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfEmployeeWorkforceLineItems_44f1647b-9cbb-4213-b2b4-b8a3447bc51b" xlink:to="loc_ifrs-full_AverageNumberOfEmployees_27ee2524-90a1-4a9b-8c84-4a13365f7409" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/FinancialgainlossNarrativeDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#FinancialgainlossNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/FinancialgainlossNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfFinancialGainLossLineItems_4e1da471-5df4-4efb-bd5e-4187070ccabd" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfFinancialGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfFinancialGainLossTable_0fcf66de-1125-412e-acd8-6b33fe527f75" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfFinancialGainLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_abvx_DisclosureOfFinancialGainLossLineItems_4e1da471-5df4-4efb-bd5e-4187070ccabd" xlink:to="loc_abvx_DisclosureOfFinancialGainLossTable_0fcf66de-1125-412e-acd8-6b33fe527f75" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CurrencyAxis_6f343a6a-f9a3-4c85-b478-874ed8fc6d07" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CurrencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfFinancialGainLossTable_0fcf66de-1125-412e-acd8-6b33fe527f75" xlink:to="loc_srt_CurrencyAxis_6f343a6a-f9a3-4c85-b478-874ed8fc6d07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_6f343a6a-f9a3-4c85-b478-874ed8fc6d07_default" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CurrencyAxis_6f343a6a-f9a3-4c85-b478-874ed8fc6d07" xlink:to="loc_currency_AllCurrenciesDomain_6f343a6a-f9a3-4c85-b478-874ed8fc6d07_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_3f5f37fa-3993-4559-ac29-b36cfacad49c" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CurrencyAxis_6f343a6a-f9a3-4c85-b478-874ed8fc6d07" xlink:to="loc_currency_AllCurrenciesDomain_3f5f37fa-3993-4559-ac29-b36cfacad49c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_USD_e51b2326-8f4c-45a8-80b1-bb1fae735932" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_USD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_3f5f37fa-3993-4559-ac29-b36cfacad49c" xlink:to="loc_currency_USD_e51b2326-8f4c-45a8-80b1-bb1fae735932" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialInstrumentsAxis_019d0058-fb69-713d-abcf-d4e1e3a7a672" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialInstrumentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfFinancialGainLossTable_0fcf66de-1125-412e-acd8-6b33fe527f75" xlink:to="loc_ifrs-full_ClassesOfFinancialInstrumentsAxis_019d0058-fb69-713d-abcf-d4e1e3a7a672" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialInstrumentsDomain_019d0058-fb69-713d-abcf-d4e1e3a7a672_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialInstrumentsAxis_019d0058-fb69-713d-abcf-d4e1e3a7a672" xlink:to="loc_ifrs-full_ClassesOfFinancialInstrumentsDomain_019d0058-fb69-713d-abcf-d4e1e3a7a672_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialInstrumentsDomain_019d0058-fb69-7e0d-904f-0090cd8dd3ed" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialInstrumentsAxis_019d0058-fb69-713d-abcf-d4e1e3a7a672" xlink:to="loc_ifrs-full_ClassesOfFinancialInstrumentsDomain_019d0058-fb69-7e0d-904f-0090cd8dd3ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingBSAMember_019d0059-395f-7f81-b0c5-2ae1b6047179" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingBSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialInstrumentsDomain_019d0058-fb69-7e0d-904f-0090cd8dd3ed" xlink:to="loc_abvx_KreosClaretFinancingBSAMember_019d0059-395f-7f81-b0c5-2ae1b6047179" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretMinimumReturnIndemnificationsMember_019d005b-137d-7ea1-8b6e-9d6097a97088" xlink:href="abvx-20251231.xsd#abvx_KreosClaretMinimumReturnIndemnificationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialInstrumentsDomain_019d0058-fb69-7e0d-904f-0090cd8dd3ed" xlink:to="loc_abvx_KreosClaretMinimumReturnIndemnificationsMember_019d005b-137d-7ea1-8b6e-9d6097a97088" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_LossesOnChangeInFairValueOfDerivatives_019d005a-712b-7990-9b8a-b680da436521" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LossesOnChangeInFairValueOfDerivatives"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFinancialGainLossLineItems_4e1da471-5df4-4efb-bd5e-4187070ccabd" xlink:to="loc_ifrs-full_LossesOnChangeInFairValueOfDerivatives_019d005a-712b-7990-9b8a-b680da436521" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ForeignExchangeLoss_019d005c-ecef-7e97-bec8-a8b539a0fdf5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ForeignExchangeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFinancialGainLossLineItems_4e1da471-5df4-4efb-bd5e-4187070ccabd" xlink:to="loc_ifrs-full_ForeignExchangeLoss_019d005c-ecef-7e97-bec8-a8b539a0fdf5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ForeignExchangeGainsLossesOnTranslationOfForeignOperations_d185c057-1ec9-4625-8a95-3a8615d61ab9" xlink:href="abvx-20251231.xsd#abvx_ForeignExchangeGainsLossesOnTranslationOfForeignOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFinancialGainLossLineItems_4e1da471-5df4-4efb-bd5e-4187070ccabd" xlink:to="loc_abvx_ForeignExchangeGainsLossesOnTranslationOfForeignOperations_d185c057-1ec9-4625-8a95-3a8615d61ab9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_GainsOnChangeInFairValueOfDerivatives_019c5773-68de-7e7d-986b-8b2d83e5b934" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GainsOnChangeInFairValueOfDerivatives"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFinancialGainLossLineItems_4e1da471-5df4-4efb-bd5e-4187070ccabd" xlink:to="loc_ifrs-full_GainsOnChangeInFairValueOfDerivatives_019c5773-68de-7e7d-986b-8b2d83e5b934" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ForeignExchangeGain_019d005c-bf9c-7a85-a9e2-c618a72ff557" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ForeignExchangeGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfFinancialGainLossLineItems_4e1da471-5df4-4efb-bd5e-4187070ccabd" xlink:to="loc_ifrs-full_ForeignExchangeGain_019d005c-bf9c-7a85-a9e2-c618a72ff557" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/IncometaxDisclosureofdeferredtaxassetsandliabilitiesbynatureDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#IncometaxDisclosureofdeferredtaxassetsandliabilitiesbynatureDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/IncometaxDisclosureofdeferredtaxassetsandliabilitiesbynatureDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems_724dafcd-6b35-428d-9c1d-20654bcbbd40" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsTable_cfdc0a50-9734-48fc-bc1c-e0dd043a75b1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems_724dafcd-6b35-428d-9c1d-20654bcbbd40" xlink:to="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsTable_cfdc0a50-9734-48fc-bc1c-e0dd043a75b1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis_0782f2f4-8046-4980-9854-000917ee463f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsTable_cfdc0a50-9734-48fc-bc1c-e0dd043a75b1" xlink:to="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis_0782f2f4-8046-4980-9854-000917ee463f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_0782f2f4-8046-4980-9854-000917ee463f_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis_0782f2f4-8046-4980-9854-000917ee463f" xlink:to="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_0782f2f4-8046-4980-9854-000917ee463f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_e59ca16d-8b29-4770-b961-8149e0ce2b90" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis_0782f2f4-8046-4980-9854-000917ee463f" xlink:to="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_e59ca16d-8b29-4770-b961-8149e0ce2b90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RetirementBenefitObligationsRelatedTemporaryDifferencesMember_8b77ae7b-0cfd-4b2b-8753-21fb74f70af6" xlink:href="abvx-20251231.xsd#abvx_RetirementBenefitObligationsRelatedTemporaryDifferencesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_e59ca16d-8b29-4770-b961-8149e0ce2b90" xlink:to="loc_abvx_RetirementBenefitObligationsRelatedTemporaryDifferencesMember_8b77ae7b-0cfd-4b2b-8753-21fb74f70af6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SubsidiesRelatedTemporaryDifferencesMember_74255e77-d2cb-4f22-bb09-a49b7e921fd0" xlink:href="abvx-20251231.xsd#abvx_SubsidiesRelatedTemporaryDifferencesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_e59ca16d-8b29-4770-b961-8149e0ce2b90" xlink:to="loc_abvx_SubsidiesRelatedTemporaryDifferencesMember_74255e77-d2cb-4f22-bb09-a49b7e921fd0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_LeasesRelatedTemporaryDifferencesMember_3d814b11-ffba-4d11-ba62-831dcd4ab64c" xlink:href="abvx-20251231.xsd#abvx_LeasesRelatedTemporaryDifferencesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_e59ca16d-8b29-4770-b961-8149e0ce2b90" xlink:to="loc_abvx_LeasesRelatedTemporaryDifferencesMember_3d814b11-ffba-4d11-ba62-831dcd4ab64c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RoyaltyCertificatesRelatedTemporaryDifferencesMember_019c5797-a063-70d5-aab8-947b780c1504" xlink:href="abvx-20251231.xsd#abvx_RoyaltyCertificatesRelatedTemporaryDifferencesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_e59ca16d-8b29-4770-b961-8149e0ce2b90" xlink:to="loc_abvx_RoyaltyCertificatesRelatedTemporaryDifferencesMember_019c5797-a063-70d5-aab8-947b780c1504" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherFinancialLiabilitiesRelatedTemporaryDifferencesMember_73dc6f37-5229-4e55-9a88-7da81167d79e" xlink:href="abvx-20251231.xsd#abvx_OtherFinancialLiabilitiesRelatedTemporaryDifferencesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_e59ca16d-8b29-4770-b961-8149e0ce2b90" xlink:to="loc_abvx_OtherFinancialLiabilitiesRelatedTemporaryDifferencesMember_73dc6f37-5229-4e55-9a88-7da81167d79e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ProvisionsForAGATaxesRelatedTemporaryDifferencesMember_019c5785-c419-71fd-8f09-e69d0f3f7482" xlink:href="abvx-20251231.xsd#abvx_ProvisionsForAGATaxesRelatedTemporaryDifferencesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_e59ca16d-8b29-4770-b961-8149e0ce2b90" xlink:to="loc_abvx_ProvisionsForAGATaxesRelatedTemporaryDifferencesMember_019c5785-c419-71fd-8f09-e69d0f3f7482" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnusedTaxLossesMember_c1092b3d-fa04-4484-9946-0b7656afaeb3" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnusedTaxLossesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_e59ca16d-8b29-4770-b961-8149e0ce2b90" xlink:to="loc_ifrs-full_UnusedTaxLossesMember_c1092b3d-fa04-4484-9946-0b7656afaeb3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_OtherTemporaryDifferencesMember_6055f67d-dc28-48c1-b6ec-42b6f16dab44" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherTemporaryDifferencesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_e59ca16d-8b29-4770-b961-8149e0ce2b90" xlink:to="loc_ifrs-full_OtherTemporaryDifferencesMember_6055f67d-dc28-48c1-b6ec-42b6f16dab44" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DeferredTaxAssets_2af54b0e-e48b-441d-8bc1-4ab5a954ba45" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DeferredTaxAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems_724dafcd-6b35-428d-9c1d-20654bcbbd40" xlink:to="loc_ifrs-full_DeferredTaxAssets_2af54b0e-e48b-441d-8bc1-4ab5a954ba45" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DeferredTaxLiabilities_c5bfc3e7-5c5c-41c6-b78d-162faa0f633c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems_724dafcd-6b35-428d-9c1d-20654bcbbd40" xlink:to="loc_ifrs-full_DeferredTaxLiabilities_c5bfc3e7-5c5c-41c6-b78d-162faa0f633c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DeferredTaxLiabilityAsset_dd222ca8-6373-44b2-b0dc-4c49fcef96a7" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DeferredTaxLiabilityAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems_724dafcd-6b35-428d-9c1d-20654bcbbd40" xlink:to="loc_ifrs-full_DeferredTaxLiabilityAsset_dd222ca8-6373-44b2-b0dc-4c49fcef96a7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_UnrecognizedDeferredTaxAssets_bffb9a41-fee1-45f6-8f63-2e5aaf832785" xlink:href="abvx-20251231.xsd#abvx_UnrecognizedDeferredTaxAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems_724dafcd-6b35-428d-9c1d-20654bcbbd40" xlink:to="loc_abvx_UnrecognizedDeferredTaxAssets_bffb9a41-fee1-45f6-8f63-2e5aaf832785" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NetDeferredTaxAssetsLiabilitiesRecognisedInFinancialPosition_23de28d8-93e6-4680-b46c-32aef586ed00" xlink:href="abvx-20251231.xsd#abvx_NetDeferredTaxAssetsLiabilitiesRecognisedInFinancialPosition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems_724dafcd-6b35-428d-9c1d-20654bcbbd40" xlink:to="loc_abvx_NetDeferredTaxAssetsLiabilitiesRecognisedInFinancialPosition_23de28d8-93e6-4680-b46c-32aef586ed00" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/IncometaxNarrativeDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#IncometaxNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/IncometaxNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems_d6ec99ae-7a90-4adf-8579-a3b9016101f1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsTable_ef2984d7-7624-46ec-b486-63bdc1f2a554" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems_d6ec99ae-7a90-4adf-8579-a3b9016101f1" xlink:to="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsTable_ef2984d7-7624-46ec-b486-63bdc1f2a554" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_SignificantInvestmentsInSubsidiariesAxis_49bd88e9-f46d-4937-b8e4-a7284155e959" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SignificantInvestmentsInSubsidiariesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsTable_ef2984d7-7624-46ec-b486-63bdc1f2a554" xlink:to="loc_ifrs-full_SignificantInvestmentsInSubsidiariesAxis_49bd88e9-f46d-4937-b8e4-a7284155e959" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_SignificantInvestmentsInSubsidiariesDomain_49bd88e9-f46d-4937-b8e4-a7284155e959_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SignificantInvestmentsInSubsidiariesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_SignificantInvestmentsInSubsidiariesAxis_49bd88e9-f46d-4937-b8e4-a7284155e959" xlink:to="loc_ifrs-full_SignificantInvestmentsInSubsidiariesDomain_49bd88e9-f46d-4937-b8e4-a7284155e959_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_SignificantInvestmentsInSubsidiariesDomain_df20d9d7-911d-4a9c-9e7e-6584a2452da1" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SignificantInvestmentsInSubsidiariesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_SignificantInvestmentsInSubsidiariesAxis_49bd88e9-f46d-4937-b8e4-a7284155e959" xlink:to="loc_ifrs-full_SignificantInvestmentsInSubsidiariesDomain_df20d9d7-911d-4a9c-9e7e-6584a2452da1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AbivaxLLCMember_16fd3d7c-d6b3-4efa-8736-c40d322d180f" xlink:href="abvx-20251231.xsd#abvx_AbivaxLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_SignificantInvestmentsInSubsidiariesDomain_df20d9d7-911d-4a9c-9e7e-6584a2452da1" xlink:to="loc_abvx_AbivaxLLCMember_16fd3d7c-d6b3-4efa-8736-c40d322d180f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis_019c578c-c80d-74e2-8e50-a03d59e94f77" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsTable_ef2984d7-7624-46ec-b486-63bdc1f2a554" xlink:to="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis_019c578c-c80d-74e2-8e50-a03d59e94f77" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_019c578c-c80d-74e2-8e50-a03d59e94f77_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis_019c578c-c80d-74e2-8e50-a03d59e94f77" xlink:to="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_019c578c-c80d-74e2-8e50-a03d59e94f77_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_019c578c-c80d-7315-99f3-b5cd938ebeff" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis_019c578c-c80d-74e2-8e50-a03d59e94f77" xlink:to="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_019c578c-c80d-7315-99f3-b5cd938ebeff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RoyaltyCertificatesRelatedTemporaryDifferencesMember_019c5798-1a07-7e2a-a362-5fe66606b72a" xlink:href="abvx-20251231.xsd#abvx_RoyaltyCertificatesRelatedTemporaryDifferencesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsDomain_019c578c-c80d-7315-99f3-b5cd938ebeff" xlink:to="loc_abvx_RoyaltyCertificatesRelatedTemporaryDifferencesMember_019c5798-1a07-7e2a-a362-5fe66606b72a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019c5799-5262-7f8a-9711-ac7088a3b584" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsTable_ef2984d7-7624-46ec-b486-63bdc1f2a554" xlink:to="loc_srt_StatementGeographicalAxis_019c5799-5262-7f8a-9711-ac7088a3b584" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019c5799-5262-7f8a-9711-ac7088a3b584_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019c5799-5262-7f8a-9711-ac7088a3b584" xlink:to="loc_srt_SegmentGeographicalDomain_019c5799-5262-7f8a-9711-ac7088a3b584_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019c5799-5262-7060-8e3d-4276003be93f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019c5799-5262-7f8a-9711-ac7088a3b584" xlink:to="loc_srt_SegmentGeographicalDomain_019c5799-5262-7060-8e3d-4276003be93f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_FR_019c579a-18cf-7016-b0d8-d54640000e0f" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_FR"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019c5799-5262-7060-8e3d-4276003be93f" xlink:to="loc_country_FR_019c579a-18cf-7016-b0d8-d54640000e0f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DeferredTaxLiabilities_019c578c-c80d-7167-8408-14f32fe0795e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems_d6ec99ae-7a90-4adf-8579-a3b9016101f1" xlink:to="loc_ifrs-full_DeferredTaxLiabilities_019c578c-c80d-7167-8408-14f32fe0795e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DeferredTaxAssets_019c5793-a379-7aaa-84c5-f147bde633de" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DeferredTaxAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems_d6ec99ae-7a90-4adf-8579-a3b9016101f1" xlink:to="loc_ifrs-full_DeferredTaxAssets_019c5793-a379-7aaa-84c5-f147bde633de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NetDeferredTaxAssetsLiabilitiesRecognisedInFinancialPosition_019d0069-a760-7a4b-a34a-f201bc976ba9" xlink:href="abvx-20251231.xsd#abvx_NetDeferredTaxAssetsLiabilitiesRecognisedInFinancialPosition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems_d6ec99ae-7a90-4adf-8579-a3b9016101f1" xlink:to="loc_abvx_NetDeferredTaxAssetsLiabilitiesRecognisedInFinancialPosition_019d0069-a760-7a4b-a34a-f201bc976ba9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UnusedTaxLossesForWhichNoDeferredTaxAssetRecognised_06606862-9bbc-4bb3-a8f3-e2c6fe3971c4" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UnusedTaxLossesForWhichNoDeferredTaxAssetRecognised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems_d6ec99ae-7a90-4adf-8579-a3b9016101f1" xlink:to="loc_ifrs-full_UnusedTaxLossesForWhichNoDeferredTaxAssetRecognised_06606862-9bbc-4bb3-a8f3-e2c6fe3971c4" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/RelatedpartiesNarrativeDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#RelatedpartiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/RelatedpartiesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesLineItems_548bb043-bf17-43fe-9369-18043bd76570" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesTable_5351c6f2-c7fe-4196-8b19-c45cfbab0be9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesLineItems_548bb043-bf17-43fe-9369-18043bd76570" xlink:to="loc_ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesTable_5351c6f2-c7fe-4196-8b19-c45cfbab0be9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_4a89241a-3065-48d6-a921-488e9c752be6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesTable_5351c6f2-c7fe-4196-8b19-c45cfbab0be9" xlink:to="loc_srt_TitleOfIndividualAxis_4a89241a-3065-48d6-a921-488e9c752be6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_4a89241a-3065-48d6-a921-488e9c752be6_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_4a89241a-3065-48d6-a921-488e9c752be6" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_4a89241a-3065-48d6-a921-488e9c752be6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_c02fddb3-2ad6-47a9-830d-1f3515d02ab9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_4a89241a-3065-48d6-a921-488e9c752be6" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_c02fddb3-2ad6-47a9-830d-1f3515d02ab9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BoardOfDirectorsAndChiefExecutiveOfficerMember_839bfe3d-37b8-4698-829f-f14137e12e10" xlink:href="abvx-20251231.xsd#abvx_BoardOfDirectorsAndChiefExecutiveOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_c02fddb3-2ad6-47a9-830d-1f3515d02ab9" xlink:to="loc_abvx_BoardOfDirectorsAndChiefExecutiveOfficerMember_839bfe3d-37b8-4698-829f-f14137e12e10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AdvisorToTheChiefExecutiveOfficerMember_b5daffd5-2a07-471c-8b89-a9177ce39c65" xlink:href="abvx-20251231.xsd#abvx_AdvisorToTheChiefExecutiveOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_c02fddb3-2ad6-47a9-830d-1f3515d02ab9" xlink:to="loc_abvx_AdvisorToTheChiefExecutiveOfficerMember_b5daffd5-2a07-471c-8b89-a9177ce39c65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CategoriesOfRelatedPartiesAxis_8e8401fa-fa5e-4e63-aa4d-3cc95bab2fdc" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfRelatedPartiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesTable_5351c6f2-c7fe-4196-8b19-c45cfbab0be9" xlink:to="loc_ifrs-full_CategoriesOfRelatedPartiesAxis_8e8401fa-fa5e-4e63-aa4d-3cc95bab2fdc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CategoriesOfRelatedPartiesDomain_8e8401fa-fa5e-4e63-aa4d-3cc95bab2fdc_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfRelatedPartiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_CategoriesOfRelatedPartiesAxis_8e8401fa-fa5e-4e63-aa4d-3cc95bab2fdc" xlink:to="loc_ifrs-full_CategoriesOfRelatedPartiesDomain_8e8401fa-fa5e-4e63-aa4d-3cc95bab2fdc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CategoriesOfRelatedPartiesDomain_0e2a4be7-51dd-4cf8-8a2f-e778c88fbb47" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfRelatedPartiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_CategoriesOfRelatedPartiesAxis_8e8401fa-fa5e-4e63-aa4d-3cc95bab2fdc" xlink:to="loc_ifrs-full_CategoriesOfRelatedPartiesDomain_0e2a4be7-51dd-4cf8-8a2f-e778c88fbb47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_KeyManagementPersonnelOfEntityOrParentMember_0bac730b-459b-49a2-ab91-0d3d2f22e1fa" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_KeyManagementPersonnelOfEntityOrParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_CategoriesOfRelatedPartiesDomain_0e2a4be7-51dd-4cf8-8a2f-e778c88fbb47" xlink:to="loc_ifrs-full_KeyManagementPersonnelOfEntityOrParentMember_0bac730b-459b-49a2-ab91-0d3d2f22e1fa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RecognisedLiabilitiesDefinedBenefitPlan_22092d6d-410c-4768-9073-1c0f48b26794" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RecognisedLiabilitiesDefinedBenefitPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesLineItems_548bb043-bf17-43fe-9369-18043bd76570" xlink:to="loc_ifrs-full_RecognisedLiabilitiesDefinedBenefitPlan_22092d6d-410c-4768-9073-1c0f48b26794" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_KeyManagementPersonnelCompensationShorttermEmployeeBenefits_16315341-3db1-49ff-9d7c-fa5a247aafa0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_KeyManagementPersonnelCompensationShorttermEmployeeBenefits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesLineItems_548bb043-bf17-43fe-9369-18043bd76570" xlink:to="loc_ifrs-full_KeyManagementPersonnelCompensationShorttermEmployeeBenefits_16315341-3db1-49ff-9d7c-fa5a247aafa0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_KeyManagementPersonnelCompensationTerminationBenefits_6482c5d3-6789-4139-8844-5ddcd1146bf5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_KeyManagementPersonnelCompensationTerminationBenefits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesLineItems_548bb043-bf17-43fe-9369-18043bd76570" xlink:to="loc_ifrs-full_KeyManagementPersonnelCompensationTerminationBenefits_6482c5d3-6789-4139-8844-5ddcd1146bf5" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/OffbalancesheetcommitmentsgivenDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#OffbalancesheetcommitmentsgivenDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/OffbalancesheetcommitmentsgivenDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsTable_6a773e1d-176a-4b41-9cba-88d5eb6ee40f" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfOffBalanceSheetCommitmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsTable_6a773e1d-176a-4b41-9cba-88d5eb6ee40f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PrincipalAgreementsAxis_019c0012-0441-791e-a402-f17846f7739e" xlink:href="abvx-20251231.xsd#abvx_PrincipalAgreementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsTable_6a773e1d-176a-4b41-9cba-88d5eb6ee40f" xlink:to="loc_abvx_PrincipalAgreementsAxis_019c0012-0441-791e-a402-f17846f7739e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PrincipalAgreementsDomain_019c0012-0441-791e-a402-f17846f7739e_default" xlink:href="abvx-20251231.xsd#abvx_PrincipalAgreementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_abvx_PrincipalAgreementsAxis_019c0012-0441-791e-a402-f17846f7739e" xlink:to="loc_abvx_PrincipalAgreementsDomain_019c0012-0441-791e-a402-f17846f7739e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_PrincipalAgreementsDomain_019c0012-0441-7e92-9ee0-1c3da7db140e" xlink:href="abvx-20251231.xsd#abvx_PrincipalAgreementsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_abvx_PrincipalAgreementsAxis_019c0012-0441-791e-a402-f17846f7739e" xlink:to="loc_abvx_PrincipalAgreementsDomain_019c0012-0441-7e92-9ee0-1c3da7db140e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExclusiveLicensingAgreementWithCNRSUniversityOfMontpellierAndInstitutCurieMember_019c0012-0441-7c2d-9a8f-89f9e9b42c5a" xlink:href="abvx-20251231.xsd#abvx_ExclusiveLicensingAgreementWithCNRSUniversityOfMontpellierAndInstitutCurieMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_PrincipalAgreementsDomain_019c0012-0441-7e92-9ee0-1c3da7db140e" xlink:to="loc_abvx_ExclusiveLicensingAgreementWithCNRSUniversityOfMontpellierAndInstitutCurieMember_019c0012-0441-7c2d-9a8f-89f9e9b42c5a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ResearchAndCollaborationAgreementWithCNRSUniversityOfMontpellierAndInstitutCurieMember_019c0012-286d-7c14-a54c-7d1a6b1a86d3" xlink:href="abvx-20251231.xsd#abvx_ResearchAndCollaborationAgreementWithCNRSUniversityOfMontpellierAndInstitutCurieMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_PrincipalAgreementsDomain_019c0012-0441-7e92-9ee0-1c3da7db140e" xlink:to="loc_abvx_ResearchAndCollaborationAgreementWithCNRSUniversityOfMontpellierAndInstitutCurieMember_019c0012-286d-7c14-a54c-7d1a6b1a86d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_ExclusiveLicensingContractWithTheScrippsResearchInstituteUniversityOfChicagoAndBrighamYoungUniversityMember_019c0012-286d-76bd-9d5b-9d2af1576d6b" xlink:href="abvx-20251231.xsd#abvx_ExclusiveLicensingContractWithTheScrippsResearchInstituteUniversityOfChicagoAndBrighamYoungUniversityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_PrincipalAgreementsDomain_019c0012-0441-7e92-9ee0-1c3da7db140e" xlink:to="loc_abvx_ExclusiveLicensingContractWithTheScrippsResearchInstituteUniversityOfChicagoAndBrighamYoungUniversityMember_019c0012-286d-76bd-9d5b-9d2af1576d6b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019c0012-286d-7de1-89e3-698c32d87830" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsTable_6a773e1d-176a-4b41-9cba-88d5eb6ee40f" xlink:to="loc_dei_LegalEntityAxis_019c0012-286d-7de1-89e3-698c32d87830" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019c0012-286d-7de1-89e3-698c32d87830_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019c0012-286d-7de1-89e3-698c32d87830" xlink:to="loc_dei_EntityDomain_019c0012-286d-7de1-89e3-698c32d87830_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019c0012-286d-7fa3-9471-f15a6be5653b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019c0012-286d-7de1-89e3-698c32d87830" xlink:to="loc_dei_EntityDomain_019c0012-286d-7fa3-9471-f15a6be5653b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_TheScrippsResearchInstituteUniversityOfChicagoAndBrighamYoungUniversityMember_019c0012-286d-7d6f-9655-20f95ac8ad53" xlink:href="abvx-20251231.xsd#abvx_TheScrippsResearchInstituteUniversityOfChicagoAndBrighamYoungUniversityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019c0012-286d-7fa3-9471-f15a6be5653b" xlink:to="loc_abvx_TheScrippsResearchInstituteUniversityOfChicagoAndBrighamYoungUniversityMember_019c0012-286d-7d6f-9655-20f95ac8ad53" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019c0012-66f4-7709-ab1a-fc9868985fd6" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsTable_6a773e1d-176a-4b41-9cba-88d5eb6ee40f" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019c0012-66f4-7709-ab1a-fc9868985fd6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019c0012-66f4-7709-ab1a-fc9868985fd6_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019c0012-66f4-7709-ab1a-fc9868985fd6" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019c0012-66f4-7709-ab1a-fc9868985fd6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019c0012-66f4-739b-a1a4-edb123ebe044" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_019c0012-66f4-7709-ab1a-fc9868985fd6" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019c0012-66f4-739b-a1a4-edb123ebe044" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CARENAConditionalAdvanceBPIMember_019c0012-66f4-71f6-9301-3e0e44ade71f" xlink:href="abvx-20251231.xsd#abvx_CARENAConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019c0012-66f4-739b-a1a4-edb123ebe044" xlink:to="loc_abvx_CARENAConditionalAdvanceBPIMember_019c0012-66f4-71f6-9301-3e0e44ade71f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RNPVIRConditionalAdvanceBPIMember_019c0012-8a04-79bd-ad0d-b20c30ee5aea" xlink:href="abvx-20251231.xsd#abvx_RNPVIRConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019c0012-66f4-739b-a1a4-edb123ebe044" xlink:to="loc_abvx_RNPVIRConditionalAdvanceBPIMember_019c0012-8a04-79bd-ad0d-b20c30ee5aea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EbolaConditionalAdvanceBPIMember_019c0012-8a04-7921-90e1-26e11bade272" xlink:href="abvx-20251231.xsd#abvx_EbolaConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019c0012-66f4-739b-a1a4-edb123ebe044" xlink:to="loc_abvx_EbolaConditionalAdvanceBPIMember_019c0012-8a04-7921-90e1-26e11bade272" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EbolaConditionalAdvanceBPILanguedocRoussillonMember_019c0012-8a04-70f3-a660-a5e4350a2490" xlink:href="abvx-20251231.xsd#abvx_EbolaConditionalAdvanceBPILanguedocRoussillonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019c0012-66f4-739b-a1a4-edb123ebe044" xlink:to="loc_abvx_EbolaConditionalAdvanceBPILanguedocRoussillonMember_019c0012-8a04-70f3-a660-a5e4350a2490" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EbolaConditionalAdvanceBPIFranceMember_019c0012-8a04-75d2-bb8d-cb5c37d0b971" xlink:href="abvx-20251231.xsd#abvx_EbolaConditionalAdvanceBPIFranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_019c0012-66f4-739b-a1a4-edb123ebe044" xlink:to="loc_abvx_EbolaConditionalAdvanceBPIFranceMember_019c0012-8a04-75d2-bb8d-cb5c37d0b971" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019c0012-66f4-71de-abb7-714cffddd6d0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsTable_6a773e1d-176a-4b41-9cba-88d5eb6ee40f" xlink:to="loc_srt_RangeAxis_019c0012-66f4-71de-abb7-714cffddd6d0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c0012-66f4-71de-abb7-714cffddd6d0_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019c0012-66f4-71de-abb7-714cffddd6d0" xlink:to="loc_srt_RangeMember_019c0012-66f4-71de-abb7-714cffddd6d0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c0012-66f4-7191-8c9f-a9df2f0cc899" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019c0012-66f4-71de-abb7-714cffddd6d0" xlink:to="loc_srt_RangeMember_019c0012-66f4-7191-8c9f-a9df2f0cc899" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019c0012-66f4-7af9-8f34-b2f7fe54f121" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c0012-66f4-7191-8c9f-a9df2f0cc899" xlink:to="loc_srt_MinimumMember_019c0012-66f4-7af9-8f34-b2f7fe54f121" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019c0012-66f4-7195-839e-dfc08339060c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c0012-66f4-7191-8c9f-a9df2f0cc899" xlink:to="loc_srt_MaximumMember_019c0012-66f4-7195-839e-dfc08339060c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfExclusiveLicenses_019c0012-0441-75cd-9a54-1f3986ee0591" xlink:href="abvx-20251231.xsd#abvx_NumberOfExclusiveLicenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_NumberOfExclusiveLicenses_019c0012-0441-75cd-9a54-1f3986ee0591" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_AgreementPeriod_019c0012-286d-7e5c-8a2a-3a22ac161f55" xlink:href="abvx-20251231.xsd#abvx_AgreementPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_AgreementPeriod_019c0012-286d-7e5c-8a2a-3a22ac161f55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CollaborationAgreementsPotentialDevelopmentMilestonePaymentINDFiling_019c0012-286d-78e7-b2d4-2fb036be0158" xlink:href="abvx-20251231.xsd#abvx_CollaborationAgreementsPotentialDevelopmentMilestonePaymentINDFiling"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_CollaborationAgreementsPotentialDevelopmentMilestonePaymentINDFiling_019c0012-286d-78e7-b2d4-2fb036be0158" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CollaborationAgreementsPotentialDevelopmentMilestonePaymentPhase3_019c0012-286d-71f1-b769-e3840b396196" xlink:href="abvx-20251231.xsd#abvx_CollaborationAgreementsPotentialDevelopmentMilestonePaymentPhase3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_CollaborationAgreementsPotentialDevelopmentMilestonePaymentPhase3_019c0012-286d-71f1-b769-e3840b396196" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CollaborationAgreementsPotentialDevelopmentMilestonePaymentINDApproval_019c0012-286d-7916-85d2-3412baca3be9" xlink:href="abvx-20251231.xsd#abvx_CollaborationAgreementsPotentialDevelopmentMilestonePaymentINDApproval"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_CollaborationAgreementsPotentialDevelopmentMilestonePaymentINDApproval_019c0012-286d-7916-85d2-3412baca3be9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfAcademicInstitutions_019c0012-286d-7e63-a407-ab61d04cfaa0" xlink:href="abvx-20251231.xsd#abvx_NumberOfAcademicInstitutions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_NumberOfAcademicInstitutions_019c0012-286d-7e63-a407-ab61d04cfaa0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ProportionOfOwnershipInterestsHeldByNoncontrollingInterests_019c0012-286d-77ae-be8c-d7f95f5277f5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProportionOfOwnershipInterestsHeldByNoncontrollingInterests"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_ifrs-full_ProportionOfOwnershipInterestsHeldByNoncontrollingInterests_019c0012-286d-77ae-be8c-d7f95f5277f5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherFinancialLiabilitiesMaximumDrawdownCapacityIncludingInterest_019c0012-66f4-730e-8200-628bdd816b5f" xlink:href="abvx-20251231.xsd#abvx_OtherFinancialLiabilitiesMaximumDrawdownCapacityIncludingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_OtherFinancialLiabilitiesMaximumDrawdownCapacityIncludingInterest_019c0012-66f4-730e-8200-628bdd816b5f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherFinancialLiabilitiesAnnualPercentageOfProceedsFromSaleOfIntellectualPropertyRight_019c0012-66f4-7dde-8c33-20d9c80185b9" xlink:href="abvx-20251231.xsd#abvx_OtherFinancialLiabilitiesAnnualPercentageOfProceedsFromSaleOfIntellectualPropertyRight"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_OtherFinancialLiabilitiesAnnualPercentageOfProceedsFromSaleOfIntellectualPropertyRight_019c0012-66f4-7dde-8c33-20d9c80185b9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherFinancialLiabilitiesAnnualRevenueFromSaleOfProductsDevelopedPeriod_019c0012-66f4-7ad1-b8b3-3dd19346a160" xlink:href="abvx-20251231.xsd#abvx_OtherFinancialLiabilitiesAnnualRevenueFromSaleOfProductsDevelopedPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_OtherFinancialLiabilitiesAnnualRevenueFromSaleOfProductsDevelopedPeriod_019c0012-66f4-7ad1-b8b3-3dd19346a160" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherFinancialLiabilitiesPercentageOfAnnualRevenueFromSaleOfProductsDevelopedPreTaxRevenueThreshold_019c0012-66f4-7f95-ab55-240902ed5e13" xlink:href="abvx-20251231.xsd#abvx_OtherFinancialLiabilitiesPercentageOfAnnualRevenueFromSaleOfProductsDevelopedPreTaxRevenueThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_OtherFinancialLiabilitiesPercentageOfAnnualRevenueFromSaleOfProductsDevelopedPreTaxRevenueThreshold_019c0012-66f4-7f95-ab55-240902ed5e13" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherFinancialLiabilitiesPercentageOfAnnualRevenueFromSaleOfProductsDeveloped_019c0012-66f4-7f91-8c25-6f9587d58a0f" xlink:href="abvx-20251231.xsd#abvx_OtherFinancialLiabilitiesPercentageOfAnnualRevenueFromSaleOfProductsDeveloped"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_OtherFinancialLiabilitiesPercentageOfAnnualRevenueFromSaleOfProductsDeveloped_019c0012-66f4-7f91-8c25-6f9587d58a0f" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherFinancialLiabilitiesPayableAnnualRevenueFromSaleOfProductsDeveloped_019c0012-66f4-7720-ade6-b22fb965c580" xlink:href="abvx-20251231.xsd#abvx_OtherFinancialLiabilitiesPayableAnnualRevenueFromSaleOfProductsDeveloped"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_OtherFinancialLiabilitiesPayableAnnualRevenueFromSaleOfProductsDeveloped_019c0012-66f4-7720-ade6-b22fb965c580" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherFinancialLiabilitiesRepaymentPeriod_019c0012-66f4-709b-8b43-4cc13043ac96" xlink:href="abvx-20251231.xsd#abvx_OtherFinancialLiabilitiesRepaymentPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_OtherFinancialLiabilitiesRepaymentPeriod_019c0012-66f4-709b-8b43-4cc13043ac96" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RepaymentsOfConditionalAdvances_019c0012-66f4-7ae4-916e-555657b9c3a8" xlink:href="abvx-20251231.xsd#abvx_RepaymentsOfConditionalAdvances"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_RepaymentsOfConditionalAdvances_019c0012-66f4-7ae4-916e-555657b9c3a8" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_OtherFinancialLiabilitiesMaximumDrawdownCapacity_019c0012-8a04-712f-93da-9d795cd525b2" xlink:href="abvx-20251231.xsd#abvx_OtherFinancialLiabilitiesMaximumDrawdownCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_abvx_OtherFinancialLiabilitiesMaximumDrawdownCapacity_019c0012-8a04-712f-93da-9d795cd525b2" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CapitalCommitments_019c0012-b574-74a5-a0ed-0eb7695f6602" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CapitalCommitments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfOffBalanceSheetCommitmentsLineItems_019c0012-0441-7e13-b19e-b2809ee93f74" xlink:to="loc_ifrs-full_CapitalCommitments_019c0012-b574-74a5-a0ed-0eb7695f6602" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/OffbalancesheetcommitmentsreceivedandcontingentassetsDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#OffbalancesheetcommitmentsreceivedandcontingentassetsDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/OffbalancesheetcommitmentsreceivedandcontingentassetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfCommitmentsReceivedLineItems_8d67ee55-0750-4d48-816a-daa2f019e7d4" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfCommitmentsReceivedLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_DisclosureOfCommitmentsReceivedTable_93a78c3e-0433-4e6d-b335-49c4132d7b23" xlink:href="abvx-20251231.xsd#abvx_DisclosureOfCommitmentsReceivedTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_abvx_DisclosureOfCommitmentsReceivedLineItems_8d67ee55-0750-4d48-816a-daa2f019e7d4" xlink:to="loc_abvx_DisclosureOfCommitmentsReceivedTable_93a78c3e-0433-4e6d-b335-49c4132d7b23" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_d388beee-94fb-4600-ba3d-da1850cca49a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfCommitmentsReceivedTable_93a78c3e-0433-4e6d-b335-49c4132d7b23" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_d388beee-94fb-4600-ba3d-da1850cca49a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_d388beee-94fb-4600-ba3d-da1850cca49a_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_d388beee-94fb-4600-ba3d-da1850cca49a" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_d388beee-94fb-4600-ba3d-da1850cca49a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_c8f353ce-8653-41e0-a11d-048c9626cbb9" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesAxis_d388beee-94fb-4600-ba3d-da1850cca49a" xlink:to="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_c8f353ce-8653-41e0-a11d-048c9626cbb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_RNPVIRConditionalAdvanceBPIMember_297920cf-1823-4f19-920e-2a0b76bd1553" xlink:href="abvx-20251231.xsd#abvx_RNPVIRConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_c8f353ce-8653-41e0-a11d-048c9626cbb9" xlink:to="loc_abvx_RNPVIRConditionalAdvanceBPIMember_297920cf-1823-4f19-920e-2a0b76bd1553" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_CARENAConditionalAdvanceBPIMember_29a6f2b9-bf98-4a30-8e92-65e906fb3762" xlink:href="abvx-20251231.xsd#abvx_CARENAConditionalAdvanceBPIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_ClassesOfFinancialLiabilitiesDomain_c8f353ce-8653-41e0-a11d-048c9626cbb9" xlink:to="loc_abvx_CARENAConditionalAdvanceBPIMember_29a6f2b9-bf98-4a30-8e92-65e906fb3762" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_46a90a92-70ed-4168-94b5-92ce803b0153" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_abvx_DisclosureOfCommitmentsReceivedTable_93a78c3e-0433-4e6d-b335-49c4132d7b23" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_46a90a92-70ed-4168-94b5-92ce803b0153" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_46a90a92-70ed-4168-94b5-92ce803b0153_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_46a90a92-70ed-4168-94b5-92ce803b0153" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_46a90a92-70ed-4168-94b5-92ce803b0153_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_be095b72-f9c6-4013-8c65-48539d324618" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_46a90a92-70ed-4168-94b5-92ce803b0153" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_be095b72-f9c6-4013-8c65-48539d324618" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingMember_98641ada-cdb0-4ef5-a125-1f3337d982ef" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_be095b72-f9c6-4013-8c65-48539d324618" xlink:to="loc_abvx_KreosClaretFinancingMember_98641ada-cdb0-4ef5-a125-1f3337d982ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_HeightsConvertibleNotesTrancheBMember_cc95cbb3-5316-4e20-9246-04dd75ca917d" xlink:href="abvx-20251231.xsd#abvx_HeightsConvertibleNotesTrancheBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_be095b72-f9c6-4013-8c65-48539d324618" xlink:to="loc_abvx_HeightsConvertibleNotesTrancheBMember_cc95cbb3-5316-4e20-9246-04dd75ca917d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_UndrawnBorrowingFacilities_0b0d3d49-885c-4029-9ee0-72ad23d3d7f0" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_UndrawnBorrowingFacilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfCommitmentsReceivedLineItems_8d67ee55-0750-4d48-816a-daa2f019e7d4" xlink:to="loc_ifrs-full_UndrawnBorrowingFacilities_0b0d3d49-885c-4029-9ee0-72ad23d3d7f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfProjectsTerminated_f4614113-362e-4b19-afc8-36852878cc99" xlink:href="abvx-20251231.xsd#abvx_NumberOfProjectsTerminated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_abvx_DisclosureOfCommitmentsReceivedLineItems_8d67ee55-0750-4d48-816a-daa2f019e7d4" xlink:to="loc_abvx_NumberOfProjectsTerminated_f4614113-362e-4b19-afc8-36852878cc99" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.abivax.com/role/ManagementandassessmentoffinancialrisksDetails" xlink:type="simple" xlink:href="abvx-20251231.xsd#ManagementandassessmentoffinancialrisksDetails"/>
  <link:definitionLink xlink:role="http://www.abivax.com/role/ManagementandassessmentoffinancialrisksDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfCreditRiskExposureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_DisclosureOfCreditRiskExposureTable_a02a0791-7ac7-4072-a071-ded250bb9e86" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfCreditRiskExposureTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_ifrs-full_DisclosureOfCreditRiskExposureTable_a02a0791-7ac7-4072-a071-ded250bb9e86" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CurrencyAxis_019c001b-755b-7f02-b92a-b8d22b20f3e3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CurrencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureTable_a02a0791-7ac7-4072-a071-ded250bb9e86" xlink:to="loc_srt_CurrencyAxis_019c001b-755b-7f02-b92a-b8d22b20f3e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_019c001b-755b-7f02-b92a-b8d22b20f3e3_default" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CurrencyAxis_019c001b-755b-7f02-b92a-b8d22b20f3e3" xlink:to="loc_currency_AllCurrenciesDomain_019c001b-755b-7f02-b92a-b8d22b20f3e3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_019c001b-755b-73f7-bcfa-58d352aeb2de" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CurrencyAxis_019c001b-755b-7f02-b92a-b8d22b20f3e3" xlink:to="loc_currency_AllCurrenciesDomain_019c001b-755b-73f7-bcfa-58d352aeb2de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_USD_019c001b-755b-774b-8c0b-5b10122c36b7" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_USD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_019c001b-755b-73f7-bcfa-58d352aeb2de" xlink:to="loc_currency_USD_019c001b-755b-774b-8c0b-5b10122c36b7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfRisksAxis_019c001b-755b-7b70-9678-ecd25b58f54e" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfRisksAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureTable_a02a0791-7ac7-4072-a071-ded250bb9e86" xlink:to="loc_ifrs-full_TypesOfRisksAxis_019c001b-755b-7b70-9678-ecd25b58f54e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfRisksDomain_019c001b-755b-7b70-9678-ecd25b58f54e_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfRisksDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfRisksAxis_019c001b-755b-7b70-9678-ecd25b58f54e" xlink:to="loc_ifrs-full_TypesOfRisksDomain_019c001b-755b-7b70-9678-ecd25b58f54e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfRisksDomain_019c001b-755b-7982-a493-bf18707f0f1d" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfRisksDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfRisksAxis_019c001b-755b-7b70-9678-ecd25b58f54e" xlink:to="loc_ifrs-full_TypesOfRisksDomain_019c001b-755b-7982-a493-bf18707f0f1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CurrencyRiskMember_019c001b-755b-7ffb-82a8-5acb8b8aa732" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CurrencyRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfRisksDomain_019c001b-755b-7982-a493-bf18707f0f1d" xlink:to="loc_ifrs-full_CurrencyRiskMember_019c001b-755b-7ffb-82a8-5acb8b8aa732" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CreditRiskMember_019c001b-755b-768d-9fef-fc9bb7577084" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CreditRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfRisksDomain_019c001b-755b-7982-a493-bf18707f0f1d" xlink:to="loc_ifrs-full_CreditRiskMember_019c001b-755b-768d-9fef-fc9bb7577084" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameAxis_019c57a0-fcda-72b4-8b39-7df9565179fd" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureTable_a02a0791-7ac7-4072-a071-ded250bb9e86" xlink:to="loc_ifrs-full_BorrowingsByNameAxis_019c57a0-fcda-72b4-8b39-7df9565179fd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019c57a0-fcda-72b4-8b39-7df9565179fd_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019c57a0-fcda-72b4-8b39-7df9565179fd" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019c57a0-fcda-72b4-8b39-7df9565179fd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsByNameDomain_019c57a0-fcda-7474-96a1-1ecfb3dd81b6" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_BorrowingsByNameAxis_019c57a0-fcda-72b4-8b39-7df9565179fd" xlink:to="loc_ifrs-full_BorrowingsByNameDomain_019c57a0-fcda-7474-96a1-1ecfb3dd81b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_KreosClaretFinancingSeniorSecuredNonConvertibleLoansMember_019c57a0-fcda-7da6-bdbe-8d302be58654" xlink:href="abvx-20251231.xsd#abvx_KreosClaretFinancingSeniorSecuredNonConvertibleLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_BorrowingsByNameDomain_019c57a0-fcda-7474-96a1-1ecfb3dd81b6" xlink:to="loc_abvx_KreosClaretFinancingSeniorSecuredNonConvertibleLoansMember_019c57a0-fcda-7da6-bdbe-8d302be58654" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfInterestRatesAxis_019c57a1-2af3-7567-a68f-2b60a1f9b8cd" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfInterestRatesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureTable_a02a0791-7ac7-4072-a071-ded250bb9e86" xlink:to="loc_ifrs-full_TypesOfInterestRatesAxis_019c57a1-2af3-7567-a68f-2b60a1f9b8cd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfInterestRatesDomain_019c57a1-2af3-7567-a68f-2b60a1f9b8cd_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfInterestRatesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_TypesOfInterestRatesAxis_019c57a1-2af3-7567-a68f-2b60a1f9b8cd" xlink:to="loc_ifrs-full_TypesOfInterestRatesDomain_019c57a1-2af3-7567-a68f-2b60a1f9b8cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TypesOfInterestRatesDomain_019c57a1-2af3-7fb6-a9af-00f3ce1829d5" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfInterestRatesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_TypesOfInterestRatesAxis_019c57a1-2af3-7567-a68f-2b60a1f9b8cd" xlink:to="loc_ifrs-full_TypesOfInterestRatesDomain_019c57a1-2af3-7fb6-a9af-00f3ce1829d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_EuropeanCentralBankBaseRateMember_019c57a1-2af3-7e5f-ab04-30a62d146e6e" xlink:href="abvx-20251231.xsd#abvx_EuropeanCentralBankBaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_TypesOfInterestRatesDomain_019c57a1-2af3-7fb6-a9af-00f3ce1829d5" xlink:to="loc_abvx_EuropeanCentralBankBaseRateMember_019c57a1-2af3-7e5f-ab04-30a62d146e6e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeAxis_019c57a2-ee66-7099-809b-1cd6bd829546" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureTable_a02a0791-7ac7-4072-a071-ded250bb9e86" xlink:to="loc_ifrs-full_RangeAxis_019c57a2-ee66-7099-809b-1cd6bd829546" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_019c57a2-ee66-7099-809b-1cd6bd829546_default" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ifrs-full_RangeAxis_019c57a2-ee66-7099-809b-1cd6bd829546" xlink:to="loc_ifrs-full_RangeDomain_019c57a2-ee66-7099-809b-1cd6bd829546_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_RangeDomain_019c57a2-ee66-7df4-a11d-cd921bdca89b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ifrs-full_RangeAxis_019c57a2-ee66-7099-809b-1cd6bd829546" xlink:to="loc_ifrs-full_RangeDomain_019c57a2-ee66-7df4-a11d-cd921bdca89b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TopOfRangeMember_019c57a3-3799-77ea-8119-2fffa3df4b7c" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TopOfRangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_019c57a2-ee66-7df4-a11d-cd921bdca89b" xlink:to="loc_ifrs-full_TopOfRangeMember_019c57a3-3799-77ea-8119-2fffa3df4b7c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BottomOfRangeMember_019c57a4-25e6-73de-99de-d97edf4deb0a" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BottomOfRangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_RangeDomain_019c57a2-ee66-7df4-a11d-cd921bdca89b" xlink:to="loc_ifrs-full_BottomOfRangeMember_019c57a4-25e6-73de-99de-d97edf4deb0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_BorrowingsAdjustmentToInterestRateBasis_019c57a0-fcda-7da3-a60c-105bcb711921" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsAdjustmentToInterestRateBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_ifrs-full_BorrowingsAdjustmentToInterestRateBasis_019c57a0-fcda-7da3-a60c-105bcb711921" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BorrowingsBasisInterestRate_019c57a1-a8d9-7158-9227-d36a8b41f9ea" xlink:href="abvx-20251231.xsd#abvx_BorrowingsBasisInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_abvx_BorrowingsBasisInterestRate_019c57a1-a8d9-7158-9227-d36a8b41f9ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_InterestRateCollarRange_019c57a3-9b2d-78d8-adf7-e65b67c6e845" xlink:href="abvx-20251231.xsd#abvx_InterestRateCollarRange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_abvx_InterestRateCollarRange_019c57a3-9b2d-78d8-adf7-e65b67c6e845" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_Assets_019c001b-755b-7645-9c0a-b523c6ac2ee6" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_ifrs-full_Assets_019c001b-755b-7645-9c0a-b523c6ac2ee6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_CashAndCashEquivalents_019c001b-755b-733b-b249-6e3a9eebbfab" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CashAndCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_ifrs-full_CashAndCashEquivalents_019c001b-755b-733b-b249-6e3a9eebbfab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TradeAndOtherReceivablesDueFromRelatedParties_019cfba9-a6ba-702f-8244-77b539395e81" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TradeAndOtherReceivablesDueFromRelatedParties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_ifrs-full_TradeAndOtherReceivablesDueFromRelatedParties_019cfba9-a6ba-702f-8244-77b539395e81" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_Liabilities_019c001b-755b-7b0d-a4b1-1d016d37648f" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_ifrs-full_Liabilities_019c001b-755b-7b0d-a4b1-1d016d37648f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ifrs-full_TradeAndOtherPayablesToRelatedParties_019d1a27-a695-72fd-bf88-efe81dfbb18b" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TradeAndOtherPayablesToRelatedParties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_ifrs-full_TradeAndOtherPayablesToRelatedParties_019d1a27-a695-72fd-bf88-efe81dfbb18b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SensitivityAnalysisForTypesOfMarketRiskReasonablyPossibleChangeInRiskVariablePercent_019c001b-755b-77dd-91cc-e55af5618188" xlink:href="abvx-20251231.xsd#abvx_SensitivityAnalysisForTypesOfMarketRiskReasonablyPossibleChangeInRiskVariablePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_abvx_SensitivityAnalysisForTypesOfMarketRiskReasonablyPossibleChangeInRiskVariablePercent_019c001b-755b-77dd-91cc-e55af5618188" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SensitivityAnalysisForTypesOfMarketRisk10AdverseChangeInExchangeRateImpactOnForeignExchangeGainLoss_019c001b-755b-7b3d-8ece-fca866f0036c" xlink:href="abvx-20251231.xsd#abvx_SensitivityAnalysisForTypesOfMarketRisk10AdverseChangeInExchangeRateImpactOnForeignExchangeGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_abvx_SensitivityAnalysisForTypesOfMarketRisk10AdverseChangeInExchangeRateImpactOnForeignExchangeGainLoss_019c001b-755b-7b3d-8ece-fca866f0036c" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_SensitivityAnalysisForTypesOfMarketRisk10FavorableChangeInExchangeRateImpactOnForeignExchangeGainLoss_019c001b-755b-74fe-af00-fc9eeee58bf7" xlink:href="abvx-20251231.xsd#abvx_SensitivityAnalysisForTypesOfMarketRisk10FavorableChangeInExchangeRateImpactOnForeignExchangeGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_abvx_SensitivityAnalysisForTypesOfMarketRisk10FavorableChangeInExchangeRateImpactOnForeignExchangeGainLoss_019c001b-755b-74fe-af00-fc9eeee58bf7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_NumberOfFinancialInstitutionsToMaintainCash_019c001b-755b-7d6e-b62f-f7e794d1a25c" xlink:href="abvx-20251231.xsd#abvx_NumberOfFinancialInstitutionsToMaintainCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_abvx_NumberOfFinancialInstitutionsToMaintainCash_019c001b-755b-7d6e-b62f-f7e794d1a25c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_BalancesWithBanksInExcessOfLegallyInsuredLimit_019c001b-755b-7abd-ac82-b565f790d5a6" xlink:href="abvx-20251231.xsd#abvx_BalancesWithBanksInExcessOfLegallyInsuredLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_abvx_BalancesWithBanksInExcessOfLegallyInsuredLimit_019c001b-755b-7abd-ac82-b565f790d5a6" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_abvx_InvestmentsInMutualFundsAndStructuredNotes_019c57ac-9c30-7ef0-95ed-c507deb20efb" xlink:href="abvx-20251231.xsd#abvx_InvestmentsInMutualFundsAndStructuredNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ifrs-full_DisclosureOfCreditRiskExposureLineItems_019c001b-755b-7d1b-b305-7cdd2e05533d" xlink:to="loc_abvx_InvestmentsInMutualFundsAndStructuredNotes_019c57ac-9c30-7ef0-95ed-c507deb20efb" xlink:type="arc" order="13"/>
  </link:definitionLink>
</link:linkbase>
