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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019e1de2-c42e-7fd9-b16f-0846c3925983,g:322026e9-52af-4957-969c-cb6877436811-->
<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://emergentbiosolutions.com/role/CondensedConsolidatedStatementsofOperations" xlink:type="simple" xlink:href="ebs-20260630.xsd#CondensedConsolidatedStatementsofOperations"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/CondensedConsolidatedStatementsofOperations" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e1de2-c63e-761f-b72f-cdcd433f3fb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019e1de2-c63e-775c-a298-460a3683a6cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019e1de2-c63e-761f-b72f-cdcd433f3fb1" xlink:to="loc_us-gaap_StatementTable_019e1de2-c63e-775c-a298-460a3683a6cf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019e1de2-c63e-71f6-9cc6-20aed300f404" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e1de2-c63e-775c-a298-460a3683a6cf" xlink:to="loc_srt_ProductOrServiceAxis_019e1de2-c63e-71f6-9cc6-20aed300f404" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e1de2-c63e-71f6-9cc6-20aed300f404_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019e1de2-c63e-71f6-9cc6-20aed300f404" xlink:to="loc_srt_ProductsAndServicesDomain_019e1de2-c63e-71f6-9cc6-20aed300f404_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e1de2-c63e-70da-8a9d-18e15d8b7a65" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019e1de2-c63e-71f6-9cc6-20aed300f404" xlink:to="loc_srt_ProductsAndServicesDomain_019e1de2-c63e-70da-8a9d-18e15d8b7a65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_ProductAndServiceMember_019e1de2-c63e-7ca6-acaa-adc9d07ef6db" xlink:href="ebs-20260630.xsd#ebs_ProductAndServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e1de2-c63e-70da-8a9d-18e15d8b7a65" xlink:to="loc_ebs_ProductAndServiceMember_019e1de2-c63e-7ca6-acaa-adc9d07ef6db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_ContractsAndGrantsMember_019e1de2-c63e-743c-9474-63f6e69ce661" xlink:href="ebs-20260630.xsd#ebs_ContractsAndGrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e1de2-c63e-70da-8a9d-18e15d8b7a65" xlink:to="loc_ebs_ContractsAndGrantsMember_019e1de2-c63e-743c-9474-63f6e69ce661" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_019e1de2-c63e-768b-acc1-d41ddc06cfd9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e1de2-c63e-761f-b72f-cdcd433f3fb1" xlink:to="loc_us-gaap_RevenuesAbstract_019e1de2-c63e-768b-acc1-d41ddc06cfd9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e1de2-c63e-75d3-86ef-31e490121f52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019e1de2-c63e-768b-acc1-d41ddc06cfd9" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e1de2-c63e-75d3-86ef-31e490121f52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_019e1de2-c63e-7181-880b-09264a2e030d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e1de2-c63e-761f-b72f-cdcd433f3fb1" xlink:to="loc_us-gaap_OperatingExpensesAbstract_019e1de2-c63e-7181-880b-09264a2e030d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019e1de2-c63e-7eb6-aa80-2a6d3ed57cbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019e1de2-c63e-7181-880b-09264a2e030d" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019e1de2-c63e-7eb6-aa80-2a6d3ed57cbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019e1de2-c63e-7c16-bf24-6a71d5737168" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019e1de2-c63e-7181-880b-09264a2e030d" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019e1de2-c63e-7c16-bf24-6a71d5737168" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019e1de2-c63e-7364-bf58-f8ecdc02cde5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019e1de2-c63e-7181-880b-09264a2e030d" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019e1de2-c63e-7364-bf58-f8ecdc02cde5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019e1de2-c63e-7710-a359-efd1bf1273ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019e1de2-c63e-7181-880b-09264a2e030d" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019e1de2-c63e-7710-a359-efd1bf1273ac" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_019f896f-1031-772e-96f7-4f341fb8f063" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019e1de2-c63e-7181-880b-09264a2e030d" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_019f896f-1031-772e-96f7-4f341fb8f063" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingCostsAndExpenses_019e1de2-c63e-7fe3-a6ad-66bdc0286b17" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingCostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019e1de2-c63e-7181-880b-09264a2e030d" xlink:to="loc_us-gaap_OperatingCostsAndExpenses_019e1de2-c63e-7fe3-a6ad-66bdc0286b17" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019e1de2-c63e-7835-ab12-0281b7622935" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e1de2-c63e-761f-b72f-cdcd433f3fb1" xlink:to="loc_us-gaap_OperatingIncomeLoss_019e1de2-c63e-7835-ab12-0281b7622935" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e1de2-c63e-7322-8949-cc2b2a65c47d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e1de2-c63e-761f-b72f-cdcd433f3fb1" xlink:to="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e1de2-c63e-7322-8949-cc2b2a65c47d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019e1de2-c63e-76e2-8523-806aadbef6ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e1de2-c63e-7322-8949-cc2b2a65c47d" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019e1de2-c63e-76e2-8523-806aadbef6ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_019e1de2-c63e-7b3d-9fc7-545c62bfe5fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e1de2-c63e-7322-8949-cc2b2a65c47d" xlink:to="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_019e1de2-c63e-7b3d-9fc7-545c62bfe5fa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019fa456-c9ef-75bf-b787-bb073d22ff30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e1de2-c63e-7322-8949-cc2b2a65c47d" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019fa456-c9ef-75bf-b787-bb073d22ff30" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019e1de2-c63e-7e03-a796-2dbd9f80a7b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e1de2-c63e-7322-8949-cc2b2a65c47d" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019e1de2-c63e-7e03-a796-2dbd9f80a7b6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019e1de2-c63e-704b-9433-95ed5637c458" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e1de2-c63e-7322-8949-cc2b2a65c47d" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019e1de2-c63e-704b-9433-95ed5637c458" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019e1de2-c63e-7151-9365-1c1a76765da7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e1de2-c63e-761f-b72f-cdcd433f3fb1" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019e1de2-c63e-7151-9365-1c1a76765da7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019e1de2-c63e-73fa-b908-e42569a0d22f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e1de2-c63e-761f-b72f-cdcd433f3fb1" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019e1de2-c63e-73fa-b908-e42569a0d22f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e1de2-c63e-78ff-9773-8e15c196954d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e1de2-c63e-761f-b72f-cdcd433f3fb1" xlink:to="loc_us-gaap_NetIncomeLoss_019e1de2-c63e-78ff-9773-8e15c196954d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDilutedAbstract_019e1de2-c63e-73df-af2c-d477bced9259" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDilutedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e1de2-c63e-761f-b72f-cdcd433f3fb1" xlink:to="loc_us-gaap_EarningsPerShareDilutedAbstract_019e1de2-c63e-73df-af2c-d477bced9259" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019e1de2-c63e-76aa-bb68-5385fe352b62" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedAbstract_019e1de2-c63e-73df-af2c-d477bced9259" xlink:to="loc_us-gaap_EarningsPerShareBasic_019e1de2-c63e-76aa-bb68-5385fe352b62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019e1de2-c63e-7ac0-9cf3-d27a28d8ecc8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedAbstract_019e1de2-c63e-73df-af2c-d477bced9259" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019e1de2-c63e-7ac0-9cf3-d27a28d8ecc8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019e1de2-c63e-78a6-aa4b-83b58f016e81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e1de2-c63e-761f-b72f-cdcd433f3fb1" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019e1de2-c63e-78a6-aa4b-83b58f016e81" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019e1de2-c63e-765e-a2b9-1821c63451c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019e1de2-c63e-78a6-aa4b-83b58f016e81" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019e1de2-c63e-765e-a2b9-1821c63451c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019e1de2-c63e-7243-bafd-f66023d37008" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019e1de2-c63e-78a6-aa4b-83b58f016e81" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019e1de2-c63e-7243-bafd-f66023d37008" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/CondensedConsolidatedStatementsofChangesinStockholdersEquity" xlink:type="simple" xlink:href="ebs-20260630.xsd#CondensedConsolidatedStatementsofChangesinStockholdersEquity"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/CondensedConsolidatedStatementsofChangesinStockholdersEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e1de2-c63e-724e-a612-17f7992896a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019e1de2-c63e-7ed9-8d76-0e839a1b02cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019e1de2-c63e-724e-a612-17f7992896a2" xlink:to="loc_us-gaap_StatementTable_019e1de2-c63e-7ed9-8d76-0e839a1b02cc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019e1de2-c63e-7eb8-a9a7-d0b4f4462647" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e1de2-c63e-7ed9-8d76-0e839a1b02cc" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019e1de2-c63e-7eb8-a9a7-d0b4f4462647" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e1de2-c63e-7eb8-a9a7-d0b4f4462647_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019e1de2-c63e-7eb8-a9a7-d0b4f4462647" xlink:to="loc_us-gaap_EquityComponentDomain_019e1de2-c63e-7eb8-a9a7-d0b4f4462647_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e1de2-c63e-7f2d-a736-1bd41dc26916" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019e1de2-c63e-7eb8-a9a7-d0b4f4462647" xlink:to="loc_us-gaap_EquityComponentDomain_019e1de2-c63e-7f2d-a736-1bd41dc26916" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e1de2-c63e-7998-9724-c328ccf0fe79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e1de2-c63e-7f2d-a736-1bd41dc26916" xlink:to="loc_us-gaap_CommonStockMember_019e1de2-c63e-7998-9724-c328ccf0fe79" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_019e1de2-c63e-718d-b033-c445d21e6afc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e1de2-c63e-7f2d-a736-1bd41dc26916" xlink:to="loc_us-gaap_TreasuryStockCommonMember_019e1de2-c63e-718d-b033-c445d21e6afc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019e1de2-c63e-7e9d-b00c-fe542c4496fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e1de2-c63e-7f2d-a736-1bd41dc26916" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019e1de2-c63e-7e9d-b00c-fe542c4496fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e1de2-c63e-7819-a612-56e6bf9bafd5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e1de2-c63e-7f2d-a736-1bd41dc26916" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e1de2-c63e-7819-a612-56e6bf9bafd5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019e1de2-c63e-733a-8bfe-16bc0e9b772b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e1de2-c63e-7f2d-a736-1bd41dc26916" xlink:to="loc_us-gaap_RetainedEarningsMember_019e1de2-c63e-733a-8bfe-16bc0e9b772b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e1de2-c63e-7e61-bf49-8a83c7b9ce10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e1de2-c63e-724e-a612-17f7992896a2" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e1de2-c63e-7e61-bf49-8a83c7b9ce10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019e1de2-c63e-7cd0-b270-98829c4cecdf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e1de2-c63e-7e61-bf49-8a83c7b9ce10" xlink:to="loc_us-gaap_CommonStockSharesIssued_019e1de2-c63e-7cd0-b270-98829c4cecdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019e1de2-c63e-7671-ade6-f84936999b7f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e1de2-c63e-7e61-bf49-8a83c7b9ce10" xlink:to="loc_us-gaap_StockholdersEquity_019e1de2-c63e-7671-ade6-f84936999b7f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019e1de2-c63e-7bbe-90df-8e4de54cbc4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e1de2-c63e-7e61-bf49-8a83c7b9ce10" xlink:to="loc_us-gaap_TreasuryStockCommonShares_019e1de2-c63e-7bbe-90df-8e4de54cbc4c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e1de2-c63e-7f1f-9f49-93fe7422ff1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e1de2-c63e-7e61-bf49-8a83c7b9ce10" xlink:to="loc_us-gaap_NetIncomeLoss_019e1de2-c63e-7f1f-9f49-93fe7422ff1e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019e1de2-c63e-7368-be83-4ffcccf54642" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e1de2-c63e-7e61-bf49-8a83c7b9ce10" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019e1de2-c63e-7368-be83-4ffcccf54642" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019e1de2-c63e-7369-b71b-8751c932542b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e1de2-c63e-7e61-bf49-8a83c7b9ce10" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019e1de2-c63e-7369-b71b-8751c932542b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_019e1de2-c63e-7998-863d-0db6ddb2be52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e1de2-c63e-7e61-bf49-8a83c7b9ce10" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_019e1de2-c63e-7998-863d-0db6ddb2be52" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_019e1de2-c63e-788d-ae76-c6b147bde168" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e1de2-c63e-7e61-bf49-8a83c7b9ce10" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_019e1de2-c63e-788d-ae76-c6b147bde168" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019e1de2-c63e-710a-8f54-3625e79066c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e1de2-c63e-7e61-bf49-8a83c7b9ce10" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019e1de2-c63e-710a-8f54-3625e79066c5" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019e1de2-c63e-77b6-80d6-f81e9dfc0776" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019e1de2-c63e-7666-9147-3f06306b55b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019e1de2-c63e-72e1-ba69-e914fab7b1ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/AssetsheldforsaleNarrativeDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#AssetsheldforsaleNarrativeDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/AssetsheldforsaleNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e1de2-c712-76cd-9aa9-2e31fdbfdabd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e1de2-c712-7204-8365-7aa957296b7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e1de2-c712-76cd-9aa9-2e31fdbfdabd" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e1de2-c712-7204-8365-7aa957296b7e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c712-7e78-840c-97124422d99e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e1de2-c712-7204-8365-7aa957296b7e" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c712-7e78-840c-97124422d99e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c712-7e78-840c-97124422d99e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c712-7e78-840c-97124422d99e" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c712-7e78-840c-97124422d99e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c712-7e1b-8601-f8f60fbdde26" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c712-7e78-840c-97124422d99e" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c712-7e1b-8601-f8f60fbdde26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember_019f471e-8c44-7439-9fbf-1d400b0e273f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c712-7e1b-8601-f8f60fbdde26" xlink:to="loc_us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember_019f471e-8c44-7439-9fbf-1d400b0e273f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c712-73fb-b584-2caf95603fea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e1de2-c712-7204-8365-7aa957296b7e" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c712-73fb-b584-2caf95603fea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c712-73fb-b584-2caf95603fea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c712-73fb-b584-2caf95603fea" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c712-73fb-b584-2caf95603fea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c712-75ac-a838-ecb86382d8ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c712-73fb-b584-2caf95603fea" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c712-75ac-a838-ecb86382d8ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_OfficePropertyGaithersburgMarylandMember_019f41dd-0f97-71e6-bbd0-b5bb7a8ab121" xlink:href="ebs-20260630.xsd#ebs_OfficePropertyGaithersburgMarylandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c712-75ac-a838-ecb86382d8ac" xlink:to="loc_ebs_OfficePropertyGaithersburgMarylandMember_019f41dd-0f97-71e6-bbd0-b5bb7a8ab121" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_019f41e3-94f5-7255-b42c-b4203035c80e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e1de2-c712-76cd-9aa9-2e31fdbfdabd" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_019f41e3-94f5-7255-b42c-b4203035c80e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_019f8b6a-1841-7b03-86aa-c1fab945aaea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e1de2-c712-76cd-9aa9-2e31fdbfdabd" xlink:to="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_019f8b6a-1841-7b03-86aa-c1fab945aaea" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/AssetsheldforsaleScheduleofassetsheldforsaleDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#AssetsheldforsaleScheduleofassetsheldforsaleDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/AssetsheldforsaleScheduleofassetsheldforsaleDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e1de2-c712-784a-9df4-aa63e2b28379" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e1de2-c712-7fcd-b456-f0044990b47c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e1de2-c712-784a-9df4-aa63e2b28379" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e1de2-c712-7fcd-b456-f0044990b47c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c712-778a-abe1-7d7df037201c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e1de2-c712-7fcd-b456-f0044990b47c" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c712-778a-abe1-7d7df037201c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c712-778a-abe1-7d7df037201c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c712-778a-abe1-7d7df037201c" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c712-778a-abe1-7d7df037201c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c712-7234-94bb-be70db537100" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c712-778a-abe1-7d7df037201c" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c712-7234-94bb-be70db537100" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember_019f4721-0566-79ad-b661-cd728821fb93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c712-7234-94bb-be70db537100" xlink:to="loc_us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember_019f4721-0566-79ad-b661-cd728821fb93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c712-762a-abaf-f350484986de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e1de2-c712-7fcd-b456-f0044990b47c" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c712-762a-abaf-f350484986de" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c712-762a-abaf-f350484986de_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c712-762a-abaf-f350484986de" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c712-762a-abaf-f350484986de_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c712-7b73-a6ba-5e066e5e1afb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c712-762a-abaf-f350484986de" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c712-7b73-a6ba-5e066e5e1afb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_OfficePropertyGaithersburgMarylandMember_019e1de2-c712-78ab-bb20-2180212a5808" xlink:href="ebs-20260630.xsd#ebs_OfficePropertyGaithersburgMarylandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c712-7b73-a6ba-5e066e5e1afb" xlink:to="loc_ebs_OfficePropertyGaithersburgMarylandMember_019e1de2-c712-78ab-bb20-2180212a5808" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_019e1de2-c712-7fef-90ef-2f7b8799c005" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e1de2-c712-784a-9df4-aa63e2b28379" xlink:to="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_019e1de2-c712-7fef-90ef-2f7b8799c005" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationPropertyPlantAndEquipment_019e1de2-c712-721d-ab78-3fc87b27bc43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_019e1de2-c712-7fef-90ef-2f7b8799c005" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationPropertyPlantAndEquipment_019e1de2-c712-721d-ab78-3fc87b27bc43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DisposalGroupIncludingDiscontinuedOperationAssetsValuationAllowance_019e1de2-c712-7a42-b901-84f3e2125339" xlink:href="ebs-20260630.xsd#ebs_DisposalGroupIncludingDiscontinuedOperationAssetsValuationAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_019e1de2-c712-7fef-90ef-2f7b8799c005" xlink:to="loc_ebs_DisposalGroupIncludingDiscontinuedOperationAssetsValuationAllowance_019e1de2-c712-7a42-b901-84f3e2125339" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_019e1de2-c712-7d42-891d-3991fa047ee4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_019e1de2-c712-7fef-90ef-2f7b8799c005" xlink:to="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_019e1de2-c712-7d42-891d-3991fa047ee4" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/DivestituresDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#DivestituresDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/DivestituresDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e1de2-c63e-7674-883f-3e78b8d8d8c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e1de2-c63e-7048-a224-33ec0b380a0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e1de2-c63e-7674-883f-3e78b8d8d8c9" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e1de2-c63e-7048-a224-33ec0b380a0a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c63e-7638-a9f0-62aa9ef32233" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e1de2-c63e-7048-a224-33ec0b380a0a" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c63e-7638-a9f0-62aa9ef32233" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c63e-7638-a9f0-62aa9ef32233_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c63e-7638-a9f0-62aa9ef32233" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c63e-7638-a9f0-62aa9ef32233_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c63e-7925-a9e9-8b06622a4c09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c63e-7638-a9f0-62aa9ef32233" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c63e-7925-a9e9-8b06622a4c09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember_019e1de2-c63e-741b-96c5-918191960ff8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c63e-7925-a9e9-8b06622a4c09" xlink:to="loc_us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember_019e1de2-c63e-741b-96c5-918191960ff8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c63e-7928-9d56-c5902f6706f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e1de2-c63e-7048-a224-33ec0b380a0a" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c63e-7928-9d56-c5902f6706f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c63e-7928-9d56-c5902f6706f4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c63e-7928-9d56-c5902f6706f4" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c63e-7928-9d56-c5902f6706f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c63e-7ed4-84e5-1a841a4310f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c63e-7928-9d56-c5902f6706f4" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c63e-7ed4-84e5-1a841a4310f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_BaltimoreCamdenFacilityAndRSDLMember_019e4727-3388-7c72-aaab-deb9345d71b1" xlink:href="ebs-20260630.xsd#ebs_BaltimoreCamdenFacilityAndRSDLMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c63e-7ed4-84e5-1a841a4310f9" xlink:to="loc_ebs_BaltimoreCamdenFacilityAndRSDLMember_019e4727-3388-7c72-aaab-deb9345d71b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_RSDLMember_019e1de2-c63e-7948-8968-fab446a89ac3" xlink:href="ebs-20260630.xsd#ebs_RSDLMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ebs_BaltimoreCamdenFacilityAndRSDLMember_019e4727-3388-7c72-aaab-deb9345d71b1" xlink:to="loc_ebs_RSDLMember_019e1de2-c63e-7948-8968-fab446a89ac3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_TravelHealthBusinessMember_019e1de2-c63e-79ef-8eee-e4b3fbe51f6d" xlink:href="ebs-20260630.xsd#ebs_TravelHealthBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c63e-7ed4-84e5-1a841a4310f9" xlink:to="loc_ebs_TravelHealthBusinessMember_019e1de2-c63e-79ef-8eee-e4b3fbe51f6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_BaltimoreBayviewFacilityMember_019e1de2-c63e-7697-95bf-06b7e5bab3cc" xlink:href="ebs-20260630.xsd#ebs_BaltimoreBayviewFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c63e-7ed4-84e5-1a841a4310f9" xlink:to="loc_ebs_BaltimoreBayviewFacilityMember_019e1de2-c63e-7697-95bf-06b7e5bab3cc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationByTypeAxis_019e1de2-c63e-761a-87e0-37ad901af1e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContingentConsiderationByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e1de2-c63e-7048-a224-33ec0b380a0a" xlink:to="loc_us-gaap_ContingentConsiderationByTypeAxis_019e1de2-c63e-761a-87e0-37ad901af1e9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_019e1de2-c63e-761a-87e0-37ad901af1e9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_019e1de2-c63e-761a-87e0-37ad901af1e9" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_019e1de2-c63e-761a-87e0-37ad901af1e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_019e1de2-c63e-7642-b2e9-33b89dbf00ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_019e1de2-c63e-761a-87e0-37ad901af1e9" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_019e1de2-c63e-7642-b2e9-33b89dbf00ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DevelopmentBasedMilestonesMember_019e1de2-c63e-7e23-8150-9cd47405c276" xlink:href="ebs-20260630.xsd#ebs_DevelopmentBasedMilestonesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_019e1de2-c63e-7642-b2e9-33b89dbf00ec" xlink:to="loc_ebs_DevelopmentBasedMilestonesMember_019e1de2-c63e-7e23-8150-9cd47405c276" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_SalesBasedMilestonesMember_019e1de2-c63e-7e05-aa41-e36e0329e1b9" xlink:href="ebs-20260630.xsd#ebs_SalesBasedMilestonesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_019e1de2-c63e-7642-b2e9-33b89dbf00ec" xlink:to="loc_ebs_SalesBasedMilestonesMember_019e1de2-c63e-7e05-aa41-e36e0329e1b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e1de2-c63e-747e-9512-5c13c759936e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e1de2-c63e-7674-883f-3e78b8d8d8c9" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e1de2-c63e-747e-9512-5c13c759936e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DisposalGroupIncludingDiscontinuedOperationMaximumContingentConsiderationReceivable_019e1de2-c63e-7e7d-9780-a9b1769a9478" xlink:href="ebs-20260630.xsd#ebs_DisposalGroupIncludingDiscontinuedOperationMaximumContingentConsiderationReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e1de2-c63e-7674-883f-3e78b8d8d8c9" xlink:to="loc_ebs_DisposalGroupIncludingDiscontinuedOperationMaximumContingentConsiderationReceivable_019e1de2-c63e-7e7d-9780-a9b1769a9478" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019e1de2-c63e-77f8-9df0-87de67225d63" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e1de2-c63e-7674-883f-3e78b8d8d8c9" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019e1de2-c63e-77f8-9df0-87de67225d63" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfBusiness_019e1de2-c63e-761c-8885-a212a76625ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnSaleOfBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e1de2-c63e-7674-883f-3e78b8d8d8c9" xlink:to="loc_us-gaap_GainLossOnSaleOfBusiness_019e1de2-c63e-761c-8885-a212a76625ee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DisposalGroupIncludingDiscontinuedOperationTransactionCosts_019e1de2-c63e-7482-b138-16556f5373ed" xlink:href="ebs-20260630.xsd#ebs_DisposalGroupIncludingDiscontinuedOperationTransactionCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e1de2-c63e-7674-883f-3e78b8d8d8c9" xlink:to="loc_ebs_DisposalGroupIncludingDiscontinuedOperationTransactionCosts_019e1de2-c63e-7482-b138-16556f5373ed" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/PropertyplantandequipmentnetScheduleofPropertyPlantandEquipmentDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#PropertyplantandequipmentnetScheduleofPropertyPlantandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/PropertyplantandequipmentnetScheduleofPropertyPlantandEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e1de2-c63e-7960-9260-6b7fec322a73" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e1de2-c63e-73ab-aa12-80276d8ddb42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e1de2-c63e-7960-9260-6b7fec322a73" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e1de2-c63e-73ab-aa12-80276d8ddb42" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e1de2-c63e-7fc0-a4f6-907336dbfd75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e1de2-c63e-73ab-aa12-80276d8ddb42" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e1de2-c63e-7fc0-a4f6-907336dbfd75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e1de2-c63e-7fc0-a4f6-907336dbfd75_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e1de2-c63e-7fc0-a4f6-907336dbfd75" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e1de2-c63e-7fc0-a4f6-907336dbfd75_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e1de2-c63e-75bb-bf17-3ffaabd2ab23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e1de2-c63e-7fc0-a4f6-907336dbfd75" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e1de2-c63e-75bb-bf17-3ffaabd2ab23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandAndLandImprovementsMember_019e1de2-c63e-72bf-843f-3b287ea41b52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LandAndLandImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e1de2-c63e-75bb-bf17-3ffaabd2ab23" xlink:to="loc_us-gaap_LandAndLandImprovementsMember_019e1de2-c63e-72bf-843f-3b287ea41b52" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingAndBuildingImprovementsMember_019e1de2-c63e-7956-a294-c5a152ce22f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BuildingAndBuildingImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e1de2-c63e-75bb-bf17-3ffaabd2ab23" xlink:to="loc_us-gaap_BuildingAndBuildingImprovementsMember_019e1de2-c63e-7956-a294-c5a152ce22f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_019e1de2-c63e-7032-a1a2-c1054baee93d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e1de2-c63e-75bb-bf17-3ffaabd2ab23" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_019e1de2-c63e-7032-a1a2-c1054baee93d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_019e1de2-c63e-7244-8219-b20d67e18e3b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e1de2-c63e-75bb-bf17-3ffaabd2ab23" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_019e1de2-c63e-7244-8219-b20d67e18e3b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_019e1de2-c63e-7afc-9cac-aaecb7deb629" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e1de2-c63e-75bb-bf17-3ffaabd2ab23" xlink:to="loc_us-gaap_ConstructionInProgressMember_019e1de2-c63e-7afc-9cac-aaecb7deb629" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_019e1de2-c63e-7ca8-a165-12d0eb52d784" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e1de2-c63e-7960-9260-6b7fec322a73" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_019e1de2-c63e-7ca8-a165-12d0eb52d784" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019e1de2-c63e-770d-9721-51cbdcbea087" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_019e1de2-c63e-7ca8-a165-12d0eb52d784" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019e1de2-c63e-770d-9721-51cbdcbea087" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019e1de2-c63e-75e3-9205-08b919057fd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_019e1de2-c63e-7ca8-a165-12d0eb52d784" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019e1de2-c63e-75e3-9205-08b919057fd2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019e1de2-c63e-7927-b979-3d6f00e71c68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_019e1de2-c63e-7ca8-a165-12d0eb52d784" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019e1de2-c63e-7927-b979-3d6f00e71c68" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/PropertyplantandequipmentNarrativeDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#PropertyplantandequipmentNarrativeDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/PropertyplantandequipmentNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e1de2-c63e-776a-8551-535833c8ce71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e1de2-c63e-7887-b598-490e1859d784" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e1de2-c63e-776a-8551-535833c8ce71" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e1de2-c63e-7887-b598-490e1859d784" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c63e-7eff-8755-630eacbad969" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e1de2-c63e-7887-b598-490e1859d784" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c63e-7eff-8755-630eacbad969" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c63e-7eff-8755-630eacbad969_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c63e-7eff-8755-630eacbad969" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c63e-7eff-8755-630eacbad969_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c63e-710b-aa44-c18782280d72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019e1de2-c63e-7eff-8755-630eacbad969" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c63e-710b-aa44-c18782280d72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember_019e1de2-c63e-7d9c-b757-6c98407e0534" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_019e1de2-c63e-710b-aa44-c18782280d72" xlink:to="loc_us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember_019e1de2-c63e-7d9c-b757-6c98407e0534" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c63e-731e-a36f-31b5aaf76c19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e1de2-c63e-7887-b598-490e1859d784" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c63e-731e-a36f-31b5aaf76c19" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c63e-731e-a36f-31b5aaf76c19_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c63e-731e-a36f-31b5aaf76c19" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c63e-731e-a36f-31b5aaf76c19_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c63e-73c1-bf1b-1de4d420a16d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e1de2-c63e-731e-a36f-31b5aaf76c19" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c63e-73c1-bf1b-1de4d420a16d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_BioservicesMember_019e1de2-c63e-781a-92bb-13c08d46b3ae" xlink:href="ebs-20260630.xsd#ebs_BioservicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e1de2-c63e-73c1-bf1b-1de4d420a16d" xlink:to="loc_ebs_BioservicesMember_019e1de2-c63e-781a-92bb-13c08d46b3ae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_019e1de2-c63e-7605-a3e4-e054ccc30ef1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e1de2-c63e-776a-8551-535833c8ce71" xlink:to="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_019e1de2-c63e-7605-a3e4-e054ccc30ef1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/IntangibleassetsnetNarrativeDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#IntangibleassetsnetNarrativeDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/IntangibleassetsnetNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e1de2-c711-7dc5-94db-48557cd78e9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e1de2-c711-7b2a-8ea3-1ede89173dc1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e1de2-c711-7dc5-94db-48557cd78e9d" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e1de2-c711-7b2a-8ea3-1ede89173dc1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionAxis_019e1de2-c711-743b-ae0a-9388f8ab9c7a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e1de2-c711-7b2a-8ea3-1ede89173dc1" xlink:to="loc_us-gaap_AssetAcquisitionAxis_019e1de2-c711-743b-ae0a-9388f8ab9c7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_019e1de2-c711-743b-ae0a-9388f8ab9c7a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AssetAcquisitionAxis_019e1de2-c711-743b-ae0a-9388f8ab9c7a" xlink:to="loc_us-gaap_AssetAcquisitionDomain_019e1de2-c711-743b-ae0a-9388f8ab9c7a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_019e1de2-c711-7ab7-975f-35bf9d701110" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AssetAcquisitionAxis_019e1de2-c711-743b-ae0a-9388f8ab9c7a" xlink:to="loc_us-gaap_AssetAcquisitionDomain_019e1de2-c711-7ab7-975f-35bf9d701110" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_RidgebackMember_019e1de2-c711-78d1-a588-eb6346918f2c" xlink:href="ebs-20260630.xsd#ebs_RidgebackMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionDomain_019e1de2-c711-7ab7-975f-35bf9d701110" xlink:to="loc_ebs_RidgebackMember_019e1de2-c711-78d1-a588-eb6346918f2c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fa58f-7916-769c-9f68-2992d3428c22" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e1de2-c711-7b2a-8ea3-1ede89173dc1" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fa58f-7916-769c-9f68-2992d3428c22" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fa58f-7916-769c-9f68-2992d3428c22_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fa58f-7916-769c-9f68-2992d3428c22" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fa58f-7916-769c-9f68-2992d3428c22_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fa58f-7916-7e9a-9f8f-352c9a98381c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019fa58f-7916-769c-9f68-2992d3428c22" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fa58f-7916-7e9a-9f8f-352c9a98381c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_NARCANMember_019fa58f-7fa4-7101-a880-3ad661fba5bb" xlink:href="ebs-20260630.xsd#ebs_NARCANMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019fa58f-7916-7e9a-9f8f-352c9a98381c" xlink:to="loc_ebs_NARCANMember_019fa58f-7fa4-7101-a880-3ad661fba5bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fa590-8e84-7724-bfeb-82f35b2201fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e1de2-c711-7b2a-8ea3-1ede89173dc1" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fa590-8e84-7724-bfeb-82f35b2201fd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fa590-8e84-7724-bfeb-82f35b2201fd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fa590-8e84-7724-bfeb-82f35b2201fd" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fa590-8e84-7724-bfeb-82f35b2201fd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fa590-8e84-7f5c-93c0-4fb5b43018b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fa590-8e84-7724-bfeb-82f35b2201fd" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fa590-8e84-7f5c-93c0-4fb5b43018b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_NARCANMember_019fa590-d57c-761e-ba6d-b2baecbaa4a2" xlink:href="ebs-20260630.xsd#ebs_NARCANMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fa590-8e84-7f5c-93c0-4fb5b43018b3" xlink:to="loc_ebs_NARCANMember_019fa590-d57c-761e-ba6d-b2baecbaa4a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionContingentConsiderationLiabilityCurrent_019e1de2-c711-7a38-8ee8-631aa3558344" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetAcquisitionContingentConsiderationLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e1de2-c711-7dc5-94db-48557cd78e9d" xlink:to="loc_us-gaap_AssetAcquisitionContingentConsiderationLiabilityCurrent_019e1de2-c711-7a38-8ee8-631aa3558344" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_019f8987-d224-778d-9685-b63e2c4ce8df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e1de2-c711-7dc5-94db-48557cd78e9d" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_019f8987-d224-778d-9685-b63e2c4ce8df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019fa591-3a5e-7929-9689-aa672c60b5b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e1de2-c711-7dc5-94db-48557cd78e9d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019fa591-3a5e-7929-9689-aa672c60b5b4" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/IntangibleassetsnetScheduleofFiniteLivedIntangibleAssetsDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#IntangibleassetsnetScheduleofFiniteLivedIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/IntangibleassetsnetScheduleofFiniteLivedIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e1de2-c711-7bc7-bb83-fbc0b612f972" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e1de2-c711-745a-b40c-b0b4e106afbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e1de2-c711-7bc7-bb83-fbc0b612f972" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e1de2-c711-745a-b40c-b0b4e106afbb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e1de2-c711-7860-a21d-a22fce9dc520" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019e1de2-c711-745a-b40c-b0b4e106afbb" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e1de2-c711-7860-a21d-a22fce9dc520" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e1de2-c711-7860-a21d-a22fce9dc520_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e1de2-c711-7860-a21d-a22fce9dc520" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e1de2-c711-7860-a21d-a22fce9dc520_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e1de2-c711-79a2-89e3-8a6effde5dc7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019e1de2-c711-7860-a21d-a22fce9dc520" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e1de2-c711-79a2-89e3-8a6effde5dc7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_019e1de2-c711-7411-8a0c-083188bc6ab1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019e1de2-c711-79a2-89e3-8a6effde5dc7" xlink:to="loc_us-gaap_ProductMember_019e1de2-c711-7411-8a0c-083188bc6ab1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019e1de2-c711-7094-8543-513cf70a2b39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e1de2-c711-7bc7-bb83-fbc0b612f972" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019e1de2-c711-7094-8543-513cf70a2b39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019e1de2-c711-7d5c-858e-6b5bd706969e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e1de2-c711-7bc7-bb83-fbc0b612f972" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019e1de2-c711-7d5c-858e-6b5bd706969e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019e1de2-c711-7919-b6dd-918388175000" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e1de2-c711-7bc7-bb83-fbc0b612f972" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019e1de2-c711-7919-b6dd-918388175000" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019e1de2-c711-7424-b706-e597eb7a7edd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019e1de2-c711-7bc7-bb83-fbc0b612f972" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019e1de2-c711-7424-b706-e597eb7a7edd" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/FairvaluemeasurementsScheduleofFairValueHierarchyofAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#FairvaluemeasurementsScheduleofFairValueHierarchyofAssetsandLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/FairvaluemeasurementsScheduleofFairValueHierarchyofAssetsandLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e1de2-c711-7c45-ae79-736f344102e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e1de2-c711-7c71-8bc8-a6b4a30dfa8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e1de2-c711-7c45-ae79-736f344102e8" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e1de2-c711-7c71-8bc8-a6b4a30dfa8e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019e1de2-c711-78e2-97bf-08a554f6d0e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e1de2-c711-7c71-8bc8-a6b4a30dfa8e" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019e1de2-c711-78e2-97bf-08a554f6d0e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e1de2-c711-78e2-97bf-08a554f6d0e6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019e1de2-c711-78e2-97bf-08a554f6d0e6" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e1de2-c711-78e2-97bf-08a554f6d0e6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e1de2-c711-73a8-a8ca-30f7d29a58f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019e1de2-c711-78e2-97bf-08a554f6d0e6" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e1de2-c711-73a8-a8ca-30f7d29a58f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019e1de2-c711-7043-9cdf-ec752a5bc815" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019e1de2-c711-73a8-a8ca-30f7d29a58f1" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019e1de2-c711-7043-9cdf-ec752a5bc815" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e1de2-c711-7255-a184-e7936bed59b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e1de2-c711-7c71-8bc8-a6b4a30dfa8e" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e1de2-c711-7255-a184-e7936bed59b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e1de2-c711-7255-a184-e7936bed59b4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e1de2-c711-7255-a184-e7936bed59b4" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e1de2-c711-7255-a184-e7936bed59b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e1de2-c711-7ec4-9ca2-c7e1305826a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e1de2-c711-7255-a184-e7936bed59b4" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e1de2-c711-7ec4-9ca2-c7e1305826a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019e1de2-c711-7b49-8678-82217223e4ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e1de2-c711-7ec4-9ca2-c7e1305826a5" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019e1de2-c711-7b49-8678-82217223e4ae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019e1de2-c711-7ec7-aba7-89bdf11076a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e1de2-c711-7ec4-9ca2-c7e1305826a5" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019e1de2-c711-7ec7-aba7-89bdf11076a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019e1de2-c711-7a70-bce6-24bbca6817b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e1de2-c711-7ec4-9ca2-c7e1305826a5" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019e1de2-c711-7a70-bce6-24bbca6817b7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019e1de2-c711-788e-a6fc-93efb2801cf2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e1de2-c711-7c45-ae79-736f344102e8" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019e1de2-c711-788e-a6fc-93efb2801cf2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019e1de2-c711-77a4-a57e-0f5bc1213666" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e1de2-c711-7c45-ae79-736f344102e8" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019e1de2-c711-77a4-a57e-0f5bc1213666" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_WarrantLiabilitiesFairValueDisclosure_019e1de2-c711-7ee0-883f-75ae1b16fbc7" xlink:href="ebs-20260630.xsd#ebs_WarrantLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e1de2-c711-7c45-ae79-736f344102e8" xlink:to="loc_ebs_WarrantLiabilitiesFairValueDisclosure_019e1de2-c711-7ee0-883f-75ae1b16fbc7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_019e1de2-c711-7d86-ad22-d42d6f5a7585" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e1de2-c711-7c45-ae79-736f344102e8" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_019e1de2-c711-7d86-ad22-d42d6f5a7585" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/FairvaluemeasurementsNarrativeDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#FairvaluemeasurementsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/FairvaluemeasurementsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7038-9633-3435fcd48f11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7f0f-8273-b7a8d510f853" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7038-9633-3435fcd48f11" xlink:to="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7f0f-8273-b7a8d510f853" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c711-747f-ac9c-1a1daecc57eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7f0f-8273-b7a8d510f853" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c711-747f-ac9c-1a1daecc57eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c711-747f-ac9c-1a1daecc57eb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c711-747f-ac9c-1a1daecc57eb" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c711-747f-ac9c-1a1daecc57eb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c711-7294-8174-3e8f6b3d106d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c711-747f-ac9c-1a1daecc57eb" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c711-7294-8174-3e8f6b3d106d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_SeriesIWarrantsMember_019e1de2-c711-77f5-b96c-8a54ceec9a77" xlink:href="ebs-20260630.xsd#ebs_SeriesIWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c711-7294-8174-3e8f6b3d106d" xlink:to="loc_ebs_SeriesIWarrantsMember_019e1de2-c711-77f5-b96c-8a54ceec9a77" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_SeriesIIWarrantsMember_019e1de2-c711-7788-a0d6-3f6559a6efcd" xlink:href="ebs-20260630.xsd#ebs_SeriesIIWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c711-7294-8174-3e8f6b3d106d" xlink:to="loc_ebs_SeriesIIWarrantsMember_019e1de2-c711-7788-a0d6-3f6559a6efcd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e1de2-c711-7763-8a6a-dbc619bf69fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7f0f-8273-b7a8d510f853" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e1de2-c711-7763-8a6a-dbc619bf69fa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7763-8a6a-dbc619bf69fa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e1de2-c711-7763-8a6a-dbc619bf69fa" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7763-8a6a-dbc619bf69fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7a96-b4d1-b2afc2c5d95b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e1de2-c711-7763-8a6a-dbc619bf69fa" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7a96-b4d1-b2afc2c5d95b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_SeniorUnsecuredNotesDueAugust2028Member_019e1de2-c711-7eab-807e-6d7b047e32ee" xlink:href="ebs-20260630.xsd#ebs_SeniorUnsecuredNotesDueAugust2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7a96-b4d1-b2afc2c5d95b" xlink:to="loc_ebs_SeniorUnsecuredNotesDueAugust2028Member_019e1de2-c711-7eab-807e-6d7b047e32ee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019e1de2-c711-78e9-835b-0676dd16b822" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7f0f-8273-b7a8d510f853" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019e1de2-c711-78e9-835b-0676dd16b822" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-78e9-835b-0676dd16b822_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019e1de2-c711-78e9-835b-0676dd16b822" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-78e9-835b-0676dd16b822_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-749d-b309-97400e116102" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019e1de2-c711-78e9-835b-0676dd16b822" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-749d-b309-97400e116102" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_019e1de2-c711-7216-aabd-fe1e1d0dc753" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-749d-b309-97400e116102" xlink:to="loc_us-gaap_SeniorNotesMember_019e1de2-c711-7216-aabd-fe1e1d0dc753" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019e1de2-c711-7aae-abe1-86e5f7fbeb5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7038-9633-3435fcd48f11" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019e1de2-c711-7aae-abe1-86e5f7fbeb5e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019e1de2-c711-7c20-a856-4427b3ab9775" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7038-9633-3435fcd48f11" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019e1de2-c711-7c20-a856-4427b3ab9775" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_WarrantLiabilitiesFairValueDisclosure_019e1de2-c711-705d-8b68-ced52b91984a" xlink:href="ebs-20260630.xsd#ebs_WarrantLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7038-9633-3435fcd48f11" xlink:to="loc_ebs_WarrantLiabilitiesFairValueDisclosure_019e1de2-c711-705d-8b68-ced52b91984a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019e1de2-c711-73a4-bf77-e11c7e2cfe49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7038-9633-3435fcd48f11" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019e1de2-c711-73a4-bf77-e11c7e2cfe49" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_019e1de2-c711-724f-920f-c02b100bcf0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7038-9633-3435fcd48f11" xlink:to="loc_us-gaap_LongTermDebtFairValue_019e1de2-c711-724f-920f-c02b100bcf0c" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/FairvaluemeasurementsLevel3FairValueOfCommonStockWarrantLiabilityDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#FairvaluemeasurementsLevel3FairValueOfCommonStockWarrantLiabilityDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/FairvaluemeasurementsLevel3FairValueOfCommonStockWarrantLiabilityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019e1de2-c711-7e2a-b2f2-3a22a94561ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019e1de2-c711-7951-9a82-a64534a5e029" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019e1de2-c711-7e2a-b2f2-3a22a94561ee" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019e1de2-c711-7951-9a82-a64534a5e029" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_019e1de2-c711-749e-a5bf-ebb0845c1639" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019e1de2-c711-7951-9a82-a64534a5e029" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_019e1de2-c711-749e-a5bf-ebb0845c1639" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019e1de2-c711-749e-a5bf-ebb0845c1639_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019e1de2-c711-749e-a5bf-ebb0845c1639" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019e1de2-c711-749e-a5bf-ebb0845c1639_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019e1de2-c711-7db9-9aff-2ba6e52005f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019e1de2-c711-749e-a5bf-ebb0845c1639" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019e1de2-c711-7db9-9aff-2ba6e52005f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019e1de2-c711-7e5c-b545-9efa4c3180ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019e1de2-c711-7db9-9aff-2ba6e52005f9" xlink:to="loc_us-gaap_WarrantMember_019e1de2-c711-7e5c-b545-9efa4c3180ac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019e1de2-c711-7a65-9697-94cfd9c07e5c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019e1de2-c711-7e2a-b2f2-3a22a94561ee" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019e1de2-c711-7a65-9697-94cfd9c07e5c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019e1de2-c711-7c73-bd2f-f242cacc3a6a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019e1de2-c711-7a65-9697-94cfd9c07e5c" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019e1de2-c711-7c73-bd2f-f242cacc3a6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019e1de2-c711-7eb1-9f91-f18b2ad0aeae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019e1de2-c711-7a65-9697-94cfd9c07e5c" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019e1de2-c711-7eb1-9f91-f18b2ad0aeae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019e1de2-c711-746b-b968-a59b14221017" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/FairvaluemeasurementsLevel3FairValueInputsInTheBlackScholesOptionPricingModelsDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#FairvaluemeasurementsLevel3FairValueInputsInTheBlackScholesOptionPricingModelsDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/FairvaluemeasurementsLevel3FairValueInputsInTheBlackScholesOptionPricingModelsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019e1de2-c711-7c74-be45-63406fc80b7f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019e1de2-c711-7697-9694-e17b4a1d2834" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019e1de2-c711-7c74-be45-63406fc80b7f" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019e1de2-c711-7697-9694-e17b4a1d2834" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019e1de2-c711-7ba2-94e9-79800cd5e556" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019e1de2-c711-7697-9694-e17b4a1d2834" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019e1de2-c711-7ba2-94e9-79800cd5e556" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019e1de2-c711-7ba2-94e9-79800cd5e556_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019e1de2-c711-7ba2-94e9-79800cd5e556" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019e1de2-c711-7ba2-94e9-79800cd5e556_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019e1de2-c711-7f56-a8ab-d0ba4abfadf0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019e1de2-c711-7ba2-94e9-79800cd5e556" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019e1de2-c711-7f56-a8ab-d0ba4abfadf0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_019e1de2-c711-772e-bf60-b28f4a815d39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019e1de2-c711-7f56-a8ab-d0ba4abfadf0" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_019e1de2-c711-772e-bf60-b28f4a815d39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019e1de2-c711-7d7d-ae39-3546f6e596b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019e1de2-c711-7f56-a8ab-d0ba4abfadf0" xlink:to="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019e1de2-c711-7d7d-ae39-3546f6e596b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_019e1de2-c711-7398-b947-3ccec72f60da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputPriceVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019e1de2-c711-7f56-a8ab-d0ba4abfadf0" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_019e1de2-c711-7398-b947-3ccec72f60da" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e1de2-c711-7bef-9ecb-adfc0c5c8455" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019e1de2-c711-7697-9694-e17b4a1d2834" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e1de2-c711-7bef-9ecb-adfc0c5c8455" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e1de2-c711-7bef-9ecb-adfc0c5c8455_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e1de2-c711-7bef-9ecb-adfc0c5c8455" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e1de2-c711-7bef-9ecb-adfc0c5c8455_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e1de2-c711-77ba-87d4-cd58d98ffcdd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e1de2-c711-7bef-9ecb-adfc0c5c8455" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e1de2-c711-77ba-87d4-cd58d98ffcdd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019e1de2-c711-72e9-b500-8c158dcfc17f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e1de2-c711-77ba-87d4-cd58d98ffcdd" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019e1de2-c711-72e9-b500-8c158dcfc17f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019e1de2-c711-7a05-9728-8ecc026921fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019e1de2-c711-7697-9694-e17b4a1d2834" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019e1de2-c711-7a05-9728-8ecc026921fb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019e1de2-c711-7a05-9728-8ecc026921fb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019e1de2-c711-7a05-9728-8ecc026921fb" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019e1de2-c711-7a05-9728-8ecc026921fb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019e1de2-c711-7854-a4a3-67e2c1217cf7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019e1de2-c711-7a05-9728-8ecc026921fb" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019e1de2-c711-7854-a4a3-67e2c1217cf7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_019e1de2-c711-7524-9e5e-0d4af1f92308" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019e1de2-c711-7854-a4a3-67e2c1217cf7" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_019e1de2-c711-7524-9e5e-0d4af1f92308" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_019e1de2-c711-7777-84dc-470044928d1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019e1de2-c711-7697-9694-e17b4a1d2834" xlink:to="loc_us-gaap_ValuationTechniqueAxis_019e1de2-c711-7777-84dc-470044928d1c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_019e1de2-c711-7777-84dc-470044928d1c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_019e1de2-c711-7777-84dc-470044928d1c" xlink:to="loc_us-gaap_ValuationTechniqueDomain_019e1de2-c711-7777-84dc-470044928d1c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_019e1de2-c711-75f3-9369-3739c40978fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_019e1de2-c711-7777-84dc-470044928d1c" xlink:to="loc_us-gaap_ValuationTechniqueDomain_019e1de2-c711-75f3-9369-3739c40978fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_ValuationTechniqueBlackScholesModelMember_019e1de2-c711-72e9-bc29-204051152140" xlink:href="ebs-20260630.xsd#ebs_ValuationTechniqueBlackScholesModelMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_019e1de2-c711-75f3-9369-3739c40978fc" xlink:to="loc_ebs_ValuationTechniqueBlackScholesModelMember_019e1de2-c711-72e9-bc29-204051152140" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c711-7f28-b31d-16fb8c78acd7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019e1de2-c711-7697-9694-e17b4a1d2834" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c711-7f28-b31d-16fb8c78acd7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c711-7f28-b31d-16fb8c78acd7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c711-7f28-b31d-16fb8c78acd7" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c711-7f28-b31d-16fb8c78acd7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c711-7ff5-8368-ddc5798c237f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c711-7f28-b31d-16fb8c78acd7" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c711-7ff5-8368-ddc5798c237f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_A2024WarrantsMember_019e1de2-c711-7a69-958c-4a077c3d77fd" xlink:href="ebs-20260630.xsd#ebs_A2024WarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c711-7ff5-8368-ddc5798c237f" xlink:to="loc_ebs_A2024WarrantsMember_019e1de2-c711-7a69-958c-4a077c3d77fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_019e1de2-c711-765a-8bb3-18dd8a23a318" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019e1de2-c711-7c74-be45-63406fc80b7f" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_019e1de2-c711-765a-8bb3-18dd8a23a318" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/DebtScheduleofDebtDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#DebtScheduleofDebtDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/DebtScheduleofDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-71a3-a62d-91f519f63f24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7b2e-8478-36e08f6ef880" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-71a3-a62d-91f519f63f24" xlink:to="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7b2e-8478-36e08f6ef880" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019e1de2-c711-76da-a8e0-c0841fb3d6d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7b2e-8478-36e08f6ef880" xlink:to="loc_us-gaap_CreditFacilityAxis_019e1de2-c711-76da-a8e0-c0841fb3d6d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019e1de2-c711-76da-a8e0-c0841fb3d6d8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019e1de2-c711-76da-a8e0-c0841fb3d6d8" xlink:to="loc_us-gaap_CreditFacilityDomain_019e1de2-c711-76da-a8e0-c0841fb3d6d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019e1de2-c711-7657-b7c8-7bf5c56c632b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019e1de2-c711-76da-a8e0-c0841fb3d6d8" xlink:to="loc_us-gaap_CreditFacilityDomain_019e1de2-c711-7657-b7c8-7bf5c56c632b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019e1de2-c711-7bd5-b4a1-9b02049de2d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019e1de2-c711-7657-b7c8-7bf5c56c632b" xlink:to="loc_us-gaap_SecuredDebtMember_019e1de2-c711-7bd5-b4a1-9b02049de2d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019e1de2-c711-7106-93a0-76a20583c6ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7b2e-8478-36e08f6ef880" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019e1de2-c711-7106-93a0-76a20583c6ea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-7106-93a0-76a20583c6ea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019e1de2-c711-7106-93a0-76a20583c6ea" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-7106-93a0-76a20583c6ea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-7eb1-95f1-19ee9ed58862" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019e1de2-c711-7106-93a0-76a20583c6ea" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-7eb1-95f1-19ee9ed58862" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019e1de2-c711-76cc-b4e3-1e6b333b1bf5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-7eb1-95f1-19ee9ed58862" xlink:to="loc_us-gaap_LineOfCreditMember_019e1de2-c711-76cc-b4e3-1e6b333b1bf5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_019e1de2-c711-75ec-8c00-ca1105f8f703" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-7eb1-95f1-19ee9ed58862" xlink:to="loc_us-gaap_SeniorNotesMember_019e1de2-c711-75ec-8c00-ca1105f8f703" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e1de2-c711-7b80-a4c0-414b76d4b491" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7b2e-8478-36e08f6ef880" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e1de2-c711-7b80-a4c0-414b76d4b491" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7b80-a4c0-414b76d4b491_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e1de2-c711-7b80-a4c0-414b76d4b491" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7b80-a4c0-414b76d4b491_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7db3-ae26-33ebd0d4e56a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e1de2-c711-7b80-a4c0-414b76d4b491" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7db3-ae26-33ebd0d4e56a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_InitialTermLoanMember_019f1a74-bd85-7e0e-85e8-227bfa7e4744" xlink:href="ebs-20260630.xsd#ebs_InitialTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7db3-ae26-33ebd0d4e56a" xlink:to="loc_ebs_InitialTermLoanMember_019f1a74-bd85-7e0e-85e8-227bfa7e4744" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_TermLoanDue2029Member_019e1de2-c711-72c5-a9cf-6754bee95ee2" xlink:href="ebs-20260630.xsd#ebs_TermLoanDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7db3-ae26-33ebd0d4e56a" xlink:to="loc_ebs_TermLoanDue2029Member_019e1de2-c711-72c5-a9cf-6754bee95ee2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_SeniorUnsecuredNotesDueAugust2028Member_019e1de2-c711-7dba-b210-7c20086560d4" xlink:href="ebs-20260630.xsd#ebs_SeniorUnsecuredNotesDueAugust2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7db3-ae26-33ebd0d4e56a" xlink:to="loc_ebs_SeniorUnsecuredNotesDueAugust2028Member_019e1de2-c711-7dba-b210-7c20086560d4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019e1de2-c711-7897-88c6-12186ee3b45b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-71a3-a62d-91f519f63f24" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019e1de2-c711-7897-88c6-12186ee3b45b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019e1de2-c711-714f-973f-44925bebb139" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-71a3-a62d-91f519f63f24" xlink:to="loc_us-gaap_LongTermDebt_019e1de2-c711-714f-973f-44925bebb139" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNoncurrentNet_019e1de2-c711-7bd4-a5cb-56cc11ec173c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsNoncurrentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-71a3-a62d-91f519f63f24" xlink:to="loc_us-gaap_DeferredFinanceCostsNoncurrentNet_019e1de2-c711-7bd4-a5cb-56cc11ec173c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019e1de2-c711-7741-8c64-349b9e8e7d42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-71a3-a62d-91f519f63f24" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019e1de2-c711-7741-8c64-349b9e8e7d42" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/DebtNarrativeDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#DebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/DebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019eb08a-39b8-7b23-af7d-cf4bddab02ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019eb08a-39b8-7788-ac89-24b57a5f1145" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb08a-39b8-7b23-af7d-cf4bddab02ee" xlink:to="loc_us-gaap_DebtInstrumentTable_019eb08a-39b8-7788-ac89-24b57a5f1145" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019eb08a-39b8-7936-a1cd-9a372de92a55" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019eb08a-39b8-7788-ac89-24b57a5f1145" xlink:to="loc_us-gaap_CreditFacilityAxis_019eb08a-39b8-7936-a1cd-9a372de92a55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019eb08a-39b8-7936-a1cd-9a372de92a55_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019eb08a-39b8-7936-a1cd-9a372de92a55" xlink:to="loc_us-gaap_CreditFacilityDomain_019eb08a-39b8-7936-a1cd-9a372de92a55_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019eb08a-39b8-71c8-a354-8a63d08d80e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019eb08a-39b8-7936-a1cd-9a372de92a55" xlink:to="loc_us-gaap_CreditFacilityDomain_019eb08a-39b8-71c8-a354-8a63d08d80e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019eb08a-39b8-74d5-8377-d4d8d1ee6034" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019eb08a-39b8-71c8-a354-8a63d08d80e7" xlink:to="loc_us-gaap_SecuredDebtMember_019eb08a-39b8-74d5-8377-d4d8d1ee6034" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019eb08a-39b8-7306-966c-d7a9e3f02507" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019eb08a-39b8-71c8-a354-8a63d08d80e7" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019eb08a-39b8-7306-966c-d7a9e3f02507" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019eb08a-39b8-7071-94a0-cf33645219e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019eb08a-39b8-7788-ac89-24b57a5f1145" xlink:to="loc_us-gaap_DebtInstrumentAxis_019eb08a-39b8-7071-94a0-cf33645219e0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019eb08a-39b8-7071-94a0-cf33645219e0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019eb08a-39b8-7071-94a0-cf33645219e0" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019eb08a-39b8-7071-94a0-cf33645219e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019eb08a-39b8-72f8-b169-58c55cd1bbb4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019eb08a-39b8-7071-94a0-cf33645219e0" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019eb08a-39b8-72f8-b169-58c55cd1bbb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_TermLoanMember_019eb08a-39b8-7f08-8aaa-4ea445e358ca" xlink:href="ebs-20260630.xsd#ebs_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019eb08a-39b8-72f8-b169-58c55cd1bbb4" xlink:to="loc_ebs_TermLoanMember_019eb08a-39b8-7f08-8aaa-4ea445e358ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_RevolverLoansAndDelayedDrawTermLoanDDTLMember_019f1a65-e90d-7f22-bb6b-97022d22a23f" xlink:href="ebs-20260630.xsd#ebs_RevolverLoansAndDelayedDrawTermLoanDDTLMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019eb08a-39b8-72f8-b169-58c55cd1bbb4" xlink:to="loc_ebs_RevolverLoansAndDelayedDrawTermLoanDDTLMember_019f1a65-e90d-7f22-bb6b-97022d22a23f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_RevolvingLoansMember_019f1a63-b3c8-76a4-8ef9-16e42e6cc278" xlink:href="ebs-20260630.xsd#ebs_RevolvingLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ebs_RevolverLoansAndDelayedDrawTermLoanDDTLMember_019f1a65-e90d-7f22-bb6b-97022d22a23f" xlink:to="loc_ebs_RevolvingLoansMember_019f1a63-b3c8-76a4-8ef9-16e42e6cc278" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DelayedDrawTermLoanDDTLMember_019eb08a-39b8-7482-8dd0-95825a70e771" xlink:href="ebs-20260630.xsd#ebs_DelayedDrawTermLoanDDTLMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ebs_RevolverLoansAndDelayedDrawTermLoanDDTLMember_019f1a65-e90d-7f22-bb6b-97022d22a23f" xlink:to="loc_ebs_DelayedDrawTermLoanDDTLMember_019eb08a-39b8-7482-8dd0-95825a70e771" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_SeniorUnsecuredNotesDueAugust2028Member_019f899a-6453-7efe-a511-14db68b68aac" xlink:href="ebs-20260630.xsd#ebs_SeniorUnsecuredNotesDueAugust2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019eb08a-39b8-72f8-b169-58c55cd1bbb4" xlink:to="loc_ebs_SeniorUnsecuredNotesDueAugust2028Member_019f899a-6453-7efe-a511-14db68b68aac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019eb08a-39b8-7d50-94f5-edb282365749" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019eb08a-39b8-7788-ac89-24b57a5f1145" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019eb08a-39b8-7d50-94f5-edb282365749" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019eb08a-39b8-7d50-94f5-edb282365749_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019eb08a-39b8-7d50-94f5-edb282365749" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019eb08a-39b8-7d50-94f5-edb282365749_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019eb08a-39b8-78a7-a8cb-7e6d1c93d4e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019eb08a-39b8-7d50-94f5-edb282365749" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019eb08a-39b8-78a7-a8cb-7e6d1c93d4e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019eb08a-39b8-7f17-8d16-c4a268afa09d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019eb08a-39b8-78a7-a8cb-7e6d1c93d4e6" xlink:to="loc_us-gaap_LineOfCreditMember_019eb08a-39b8-7f17-8d16-c4a268afa09d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_019f899a-6453-76d9-b0e8-44aba9efc591" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019eb08a-39b8-78a7-a8cb-7e6d1c93d4e6" xlink:to="loc_us-gaap_SeniorNotesMember_019f899a-6453-76d9-b0e8-44aba9efc591" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsGross_019f668f-9ebb-792c-a2e3-7007bbfa71bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb08a-39b8-7b23-af7d-cf4bddab02ee" xlink:to="loc_us-gaap_DeferredFinanceCostsGross_019f668f-9ebb-792c-a2e3-7007bbfa71bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNoncurrentNet_019eb08a-39b8-7459-9a43-c866eb967741" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsNoncurrentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb08a-39b8-7b23-af7d-cf4bddab02ee" xlink:to="loc_us-gaap_DeferredFinanceCostsNoncurrentNet_019eb08a-39b8-7459-9a43-c866eb967741" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019eb08b-f84b-7aa8-a401-c936aa0db0b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb08a-39b8-7b23-af7d-cf4bddab02ee" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019eb08b-f84b-7aa8-a401-c936aa0db0b2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_019f899a-6453-7d5f-81ec-303e1d182c79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRepurchasedFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019eb08a-39b8-7b23-af7d-cf4bddab02ee" xlink:to="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_019f899a-6453-7d5f-81ec-303e1d182c79" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/DebtSeniorUnsecuredNotesdue2028Details" xlink:type="simple" xlink:href="ebs-20260630.xsd#DebtSeniorUnsecuredNotesdue2028Details"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/DebtSeniorUnsecuredNotesdue2028Details" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7b1d-9336-95e512946403" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7f64-a979-bf91f027ef99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7b1d-9336-95e512946403" xlink:to="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7f64-a979-bf91f027ef99" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e1de2-c711-79cd-bdf3-f14136701756" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7f64-a979-bf91f027ef99" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e1de2-c711-79cd-bdf3-f14136701756" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-79cd-bdf3-f14136701756_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e1de2-c711-79cd-bdf3-f14136701756" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-79cd-bdf3-f14136701756_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7b82-9a76-cb4c1f315985" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e1de2-c711-79cd-bdf3-f14136701756" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7b82-9a76-cb4c1f315985" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_SeniorUnsecuredNotesDueAugust2028Member_019e1de2-c711-704b-8ed2-b296d4c5d908" xlink:href="ebs-20260630.xsd#ebs_SeniorUnsecuredNotesDueAugust2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e1de2-c711-7b82-9a76-cb4c1f315985" xlink:to="loc_ebs_SeniorUnsecuredNotesDueAugust2028Member_019e1de2-c711-704b-8ed2-b296d4c5d908" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019e1de2-c711-7084-b859-3d3ac80c4993" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7f64-a979-bf91f027ef99" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019e1de2-c711-7084-b859-3d3ac80c4993" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-7084-b859-3d3ac80c4993_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019e1de2-c711-7084-b859-3d3ac80c4993" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-7084-b859-3d3ac80c4993_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-7423-b778-9a74a4533bf3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019e1de2-c711-7084-b859-3d3ac80c4993" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-7423-b778-9a74a4533bf3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_019e1de2-c711-7342-b1fa-13669d940f78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019e1de2-c711-7423-b778-9a74a4533bf3" xlink:to="loc_us-gaap_SeniorNotesMember_019e1de2-c711-7342-b1fa-13669d940f78" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_019e1de2-c711-7577-9ef7-7b384466130d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7f64-a979-bf91f027ef99" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_019e1de2-c711-7577-9ef7-7b384466130d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019e1de2-c711-7577-9ef7-7b384466130d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_019e1de2-c711-7577-9ef7-7b384466130d" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019e1de2-c711-7577-9ef7-7b384466130d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019e1de2-c711-7f29-a89c-e24977c2c545" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_019e1de2-c711-7577-9ef7-7b384466130d" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019e1de2-c711-7f29-a89c-e24977c2c545" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_019e1de2-c711-7689-902e-f52608f5e477" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019e1de2-c711-7f29-a89c-e24977c2c545" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_019e1de2-c711-7689-902e-f52608f5e477" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_019e1de2-c711-76e1-b0d5-f49b510efe7a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPeriodTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_019e1de2-c711-7f29-a89c-e24977c2c545" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_019e1de2-c711-76e1-b0d5-f49b510efe7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e1de2-c711-76b7-8eff-7e3f32631aaf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7f64-a979-bf91f027ef99" xlink:to="loc_srt_RangeAxis_019e1de2-c711-76b7-8eff-7e3f32631aaf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e1de2-c711-76b7-8eff-7e3f32631aaf_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019e1de2-c711-76b7-8eff-7e3f32631aaf" xlink:to="loc_srt_RangeMember_019e1de2-c711-76b7-8eff-7e3f32631aaf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e1de2-c711-75f9-9b8c-1d7947acc951" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019e1de2-c711-76b7-8eff-7e3f32631aaf" xlink:to="loc_srt_RangeMember_019e1de2-c711-75f9-9b8c-1d7947acc951" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e1de2-c711-79ee-b192-eca1db2a7d25" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e1de2-c711-75f9-9b8c-1d7947acc951" xlink:to="loc_srt_MaximumMember_019e1de2-c711-79ee-b192-eca1db2a7d25" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019fae9a-5b50-7f3a-8848-3391ba0906cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7f64-a979-bf91f027ef99" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019fae9a-5b50-7f3a-8848-3391ba0906cf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019fae9a-5b50-7f3a-8848-3391ba0906cf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019fae9a-5b50-7f3a-8848-3391ba0906cf" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019fae9a-5b50-7f3a-8848-3391ba0906cf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019fae9a-5b50-7e8f-83c3-61dcc45f1bb6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019fae9a-5b50-7f3a-8848-3391ba0906cf" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019fae9a-5b50-7e8f-83c3-61dcc45f1bb6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019fae9a-7995-7377-a30f-42889431af83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019fae9a-5b50-7e8f-83c3-61dcc45f1bb6" xlink:to="loc_us-gaap_SubsequentEventMember_019fae9a-7995-7377-a30f-42889431af83" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019e1de2-c711-7d5b-88e7-3aa29ce4ec32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7b1d-9336-95e512946403" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019e1de2-c711-7d5b-88e7-3aa29ce4ec32" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019e1de2-c711-7fa7-8c6f-3edbd79dea8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7b1d-9336-95e512946403" xlink:to="loc_us-gaap_LongTermDebt_019e1de2-c711-7fa7-8c6f-3edbd79dea8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_019e1de2-c711-76d4-b713-e79664266344" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7b1d-9336-95e512946403" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_019e1de2-c711-76d4-b713-e79664266344" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_019e1de2-c711-733d-b634-0bd03f443b5c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRepurchasedFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7b1d-9336-95e512946403" xlink:to="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_019e1de2-c711-733d-b634-0bd03f443b5c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRepurchaseAmount_019e1de2-c711-79c5-a96b-d96add344cf6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRepurchaseAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7b1d-9336-95e512946403" xlink:to="loc_us-gaap_DebtInstrumentRepurchaseAmount_019e1de2-c711-79c5-a96b-d96add344cf6" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/DebtTermLoanAgreementDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#DebtTermLoanAgreementDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/DebtTermLoanAgreementDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7531-85db-ed33b7cde8ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7531-85db-ed33b7cde8ac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019eb092-5b25-75d3-a57c-97687c62de01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7531-85db-ed33b7cde8ac" xlink:to="loc_us-gaap_CreditFacilityAxis_019eb092-5b25-75d3-a57c-97687c62de01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019eb092-5b25-75d3-a57c-97687c62de01_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019eb092-5b25-75d3-a57c-97687c62de01" xlink:to="loc_us-gaap_CreditFacilityDomain_019eb092-5b25-75d3-a57c-97687c62de01_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019eb092-5b25-768d-a5d8-756b6f7f1460" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019eb092-5b25-75d3-a57c-97687c62de01" xlink:to="loc_us-gaap_CreditFacilityDomain_019eb092-5b25-768d-a5d8-756b6f7f1460" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019eb092-5b25-73d3-aef7-40a4d9a48a20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019eb092-5b25-768d-a5d8-756b6f7f1460" xlink:to="loc_us-gaap_SecuredDebtMember_019eb092-5b25-73d3-aef7-40a4d9a48a20" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019eb092-5b25-7815-99e2-2462f176c53b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7531-85db-ed33b7cde8ac" xlink:to="loc_us-gaap_DebtInstrumentAxis_019eb092-5b25-7815-99e2-2462f176c53b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019eb092-5b25-7815-99e2-2462f176c53b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019eb092-5b25-7815-99e2-2462f176c53b" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019eb092-5b25-7815-99e2-2462f176c53b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019eb092-5b25-7af1-a2d6-09bbd77beb91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019eb092-5b25-7815-99e2-2462f176c53b" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019eb092-5b25-7af1-a2d6-09bbd77beb91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_TermLoanMember_019eb092-5b25-7de5-aab1-16681d809f45" xlink:href="ebs-20260630.xsd#ebs_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019eb092-5b25-7af1-a2d6-09bbd77beb91" xlink:to="loc_ebs_TermLoanMember_019eb092-5b25-7de5-aab1-16681d809f45" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_InitialTermLoanMember_019f1a74-63b3-708d-88c2-29c6f4e9df87" xlink:href="ebs-20260630.xsd#ebs_InitialTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ebs_TermLoanMember_019eb092-5b25-7de5-aab1-16681d809f45" xlink:to="loc_ebs_InitialTermLoanMember_019f1a74-63b3-708d-88c2-29c6f4e9df87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DelayedDrawTermLoanDDTLMember_019f1a77-b9e2-7e2b-95bc-510dfe7bff63" xlink:href="ebs-20260630.xsd#ebs_DelayedDrawTermLoanDDTLMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ebs_TermLoanMember_019eb092-5b25-7de5-aab1-16681d809f45" xlink:to="loc_ebs_DelayedDrawTermLoanDDTLMember_019f1a77-b9e2-7e2b-95bc-510dfe7bff63" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_UncommittedIncrementalFacilityMember_019f1a7b-7941-7696-92f7-ed4a7eb8305e" xlink:href="ebs-20260630.xsd#ebs_UncommittedIncrementalFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ebs_TermLoanMember_019eb092-5b25-7de5-aab1-16681d809f45" xlink:to="loc_ebs_UncommittedIncrementalFacilityMember_019f1a7b-7941-7696-92f7-ed4a7eb8305e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_TermLoanAfterSecondAnniversaryThroughAndIncludingThirdAnniversaryOfClosingDateMember_019f1a86-9c06-7f85-93f9-f157dd3e8405" xlink:href="ebs-20260630.xsd#ebs_TermLoanAfterSecondAnniversaryThroughAndIncludingThirdAnniversaryOfClosingDateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ebs_TermLoanMember_019eb092-5b25-7de5-aab1-16681d809f45" xlink:to="loc_ebs_TermLoanAfterSecondAnniversaryThroughAndIncludingThirdAnniversaryOfClosingDateMember_019f1a86-9c06-7f85-93f9-f157dd3e8405" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_TermLoanAfterThirdAnniversaryThroughAndIncludingFourthAnniversaryOfClosingDateMember_019f1a87-5f8f-70e2-a80d-cef95e79475b" xlink:href="ebs-20260630.xsd#ebs_TermLoanAfterThirdAnniversaryThroughAndIncludingFourthAnniversaryOfClosingDateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ebs_TermLoanMember_019eb092-5b25-7de5-aab1-16681d809f45" xlink:to="loc_ebs_TermLoanAfterThirdAnniversaryThroughAndIncludingFourthAnniversaryOfClosingDateMember_019f1a87-5f8f-70e2-a80d-cef95e79475b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019eb092-5b25-797a-8945-bc6a2461daa4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-7531-85db-ed33b7cde8ac" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019eb092-5b25-797a-8945-bc6a2461daa4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019eb092-5b25-797a-8945-bc6a2461daa4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019eb092-5b25-797a-8945-bc6a2461daa4" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019eb092-5b25-797a-8945-bc6a2461daa4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019eb092-5b25-7fa3-a4e1-187ad9952909" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019eb092-5b25-797a-8945-bc6a2461daa4" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019eb092-5b25-7fa3-a4e1-187ad9952909" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019eb092-5b25-7657-b2c0-4ca1bf2ea030" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019eb092-5b25-7fa3-a4e1-187ad9952909" xlink:to="loc_us-gaap_LineOfCreditMember_019eb092-5b25-7657-b2c0-4ca1bf2ea030" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019eb092-5b25-76df-8fac-6cfc438d986d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019eb092-5b25-76df-8fac-6cfc438d986d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTerm_019eb092-5b25-7368-951f-384b3f3f3e2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_us-gaap_DebtInstrumentTerm_019eb092-5b25-7368-951f-384b3f3f3e2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentCovenantConsolidatedSecuredLeverageRatioMaximum_019eb092-5b25-73a1-b792-633ffd04a5ce" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentCovenantConsolidatedSecuredLeverageRatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentCovenantConsolidatedSecuredLeverageRatioMaximum_019eb092-5b25-73a1-b792-633ffd04a5ce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentFaceAmountAsPercentageOfEBITDAMaximum_019f1a7c-7cf7-7bc6-a360-5febccadd3ae" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentFaceAmountAsPercentageOfEBITDAMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentFaceAmountAsPercentageOfEBITDAMaximum_019f1a7c-7cf7-7bc6-a360-5febccadd3ae" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentVariableInterestRateFloor_019eb092-5b25-71e6-bd41-9c3aa22260c3" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentVariableInterestRateFloor"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentVariableInterestRateFloor_019eb092-5b25-71e6-bd41-9c3aa22260c3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019eb092-5b25-71ab-b46e-0a50561c02d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019eb092-5b25-71ab-b46e-0a50561c02d0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentAdditionalDefaultInterestRate_019eb092-5b25-7375-aaa2-873106059b67" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentAdditionalDefaultInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentAdditionalDefaultInterestRate_019eb092-5b25-7375-aaa2-873106059b67" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019eb092-5b25-7019-899f-0c70100a7cdf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019eb092-5b25-7019-899f-0c70100a7cdf" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentTermPeriodPriorToScheduledMaturityDateOfSeniorUnsecuredNotes_019eb092-5b25-785b-a5a5-4b569089ebf6" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentTermPeriodPriorToScheduledMaturityDateOfSeniorUnsecuredNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentTermPeriodPriorToScheduledMaturityDateOfSeniorUnsecuredNotes_019eb092-5b25-785b-a5a5-4b569089ebf6" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentMaturityDateAggregatePrincipalAmountOutstandingThreshold_019eb092-5b25-7023-8c46-8625d7411647" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentMaturityDateAggregatePrincipalAmountOutstandingThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentMaturityDateAggregatePrincipalAmountOutstandingThreshold_019eb092-5b25-7023-8c46-8625d7411647" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentCovenantLiquidityRequirementMinimum_019eb092-5b25-7298-8709-e0eb779f43a0" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentCovenantLiquidityRequirementMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentCovenantLiquidityRequirementMinimum_019eb092-5b25-7298-8709-e0eb779f43a0" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentMandatoryPrepaymentPercentageOfNetCashProceedsFromIndebtednessIncurred_019eb092-5b25-7ab5-aa2c-2e28d1b48955" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentMandatoryPrepaymentPercentageOfNetCashProceedsFromIndebtednessIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentMandatoryPrepaymentPercentageOfNetCashProceedsFromIndebtednessIncurred_019eb092-5b25-7ab5-aa2c-2e28d1b48955" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentMandatoryPrepaymentPercentageOfNetCashProceedsFromDispositionsOfPropertyAndInsuranceProceeds_019eb092-5b25-7438-8368-2d0626f5c319" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentMandatoryPrepaymentPercentageOfNetCashProceedsFromDispositionsOfPropertyAndInsuranceProceeds"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentMandatoryPrepaymentPercentageOfNetCashProceedsFromDispositionsOfPropertyAndInsuranceProceeds_019eb092-5b25-7438-8368-2d0626f5c319" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentMandatoryPrepaymentNetCashProceedsFromDispositionOfPropertyThresholdAnnualBasis_019eb092-5b25-797d-b4ed-09ef42afc430" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentMandatoryPrepaymentNetCashProceedsFromDispositionOfPropertyThresholdAnnualBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentMandatoryPrepaymentNetCashProceedsFromDispositionOfPropertyThresholdAnnualBasis_019eb092-5b25-797d-b4ed-09ef42afc430" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentMandatoryPrepaymentNetCashProceedsFromDispositionOfPropertyThresholdPerTransactionBasis_019eb092-5b25-76b3-a72d-96ca1cb5f654" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentMandatoryPrepaymentNetCashProceedsFromDispositionOfPropertyThresholdPerTransactionBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentMandatoryPrepaymentNetCashProceedsFromDispositionOfPropertyThresholdPerTransactionBasis_019eb092-5b25-76b3-a72d-96ca1cb5f654" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentMandatoryPrepaymentPercentageOfAnnualExcessCashFlow_019f1a83-b584-71dc-b17d-3273fbbe3002" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentMandatoryPrepaymentPercentageOfAnnualExcessCashFlow"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentMandatoryPrepaymentPercentageOfAnnualExcessCashFlow_019f1a83-b584-71dc-b17d-3273fbbe3002" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentPrepaymentThresholdForExcessCashFlowPayment_019eb092-5b25-776d-9f32-6523d543c079" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentPrepaymentThresholdForExcessCashFlowPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentPrepaymentThresholdForExcessCashFlowPayment_019eb092-5b25-776d-9f32-6523d543c079" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentBasisSpreadOnMakeWholePremium_019f1cf6-ed3a-703b-97f7-7a2129d4e0f5" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentBasisSpreadOnMakeWholePremium"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentBasisSpreadOnMakeWholePremium_019f1cf6-ed3a-703b-97f7-7a2129d4e0f5" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentPrepaymentPremium_019eb092-5b25-7939-8dc5-2a02b6d664dd" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentPrepaymentPremium"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_ebs_DebtInstrumentPrepaymentPremium_019eb092-5b25-7939-8dc5-2a02b6d664dd" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019eb092-5b25-7afd-b144-465a1e2aab2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-750b-86cd-1e99b9e59365" xlink:to="loc_us-gaap_LongTermDebt_019eb092-5b25-7afd-b144-465a1e2aab2e" xlink:type="arc" order="19"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/DebtRevolvingLoanAgreementDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#DebtRevolvingLoanAgreementDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/DebtRevolvingLoanAgreementDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7754-872c-3fbf259d28ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-731c-9323-c292c161efd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7754-872c-3fbf259d28ba" xlink:to="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-731c-9323-c292c161efd2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019eb09a-fa6f-707f-82f1-dc0cc8c80191" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-731c-9323-c292c161efd2" xlink:to="loc_us-gaap_CreditFacilityAxis_019eb09a-fa6f-707f-82f1-dc0cc8c80191" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019eb09a-fa6f-707f-82f1-dc0cc8c80191_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019eb09a-fa6f-707f-82f1-dc0cc8c80191" xlink:to="loc_us-gaap_CreditFacilityDomain_019eb09a-fa6f-707f-82f1-dc0cc8c80191_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019eb09a-fa6f-721c-a70f-83a042db0509" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019eb09a-fa6f-707f-82f1-dc0cc8c80191" xlink:to="loc_us-gaap_CreditFacilityDomain_019eb09a-fa6f-721c-a70f-83a042db0509" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019eb09a-fa6f-7b97-aa97-b7f38fcbc870" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019eb09a-fa6f-721c-a70f-83a042db0509" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019eb09a-fa6f-7b97-aa97-b7f38fcbc870" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BridgeLoanMember_019eb09a-fa6f-74db-b20a-8c3a4c266c37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BridgeLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019eb09a-fa6f-721c-a70f-83a042db0509" xlink:to="loc_us-gaap_BridgeLoanMember_019eb09a-fa6f-74db-b20a-8c3a4c266c37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_019eb09a-fa6f-7900-8aef-94871546f874" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019eb09a-fa6f-721c-a70f-83a042db0509" xlink:to="loc_us-gaap_LetterOfCreditMember_019eb09a-fa6f-7900-8aef-94871546f874" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019eb09a-fa6f-74c7-8560-35477ab0820f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-731c-9323-c292c161efd2" xlink:to="loc_us-gaap_DebtInstrumentAxis_019eb09a-fa6f-74c7-8560-35477ab0820f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019eb09a-fa6f-74c7-8560-35477ab0820f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019eb09a-fa6f-74c7-8560-35477ab0820f" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019eb09a-fa6f-74c7-8560-35477ab0820f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019eb09a-fa6f-7a7d-896f-a57a585c70de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019eb09a-fa6f-74c7-8560-35477ab0820f" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019eb09a-fa6f-7a7d-896f-a57a585c70de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_RevolvingLoansMember_019eb09a-fa6f-7764-b703-f9fafb245dba" xlink:href="ebs-20260630.xsd#ebs_RevolvingLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019eb09a-fa6f-7a7d-896f-a57a585c70de" xlink:to="loc_ebs_RevolvingLoansMember_019eb09a-fa6f-7764-b703-f9fafb245dba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_RevolvingLoansUntilSeptember302025Member_019eb09a-fa6f-7636-a55f-50c59d26b31e" xlink:href="ebs-20260630.xsd#ebs_RevolvingLoansUntilSeptember302025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ebs_RevolvingLoansMember_019eb09a-fa6f-7764-b703-f9fafb245dba" xlink:to="loc_ebs_RevolvingLoansUntilSeptember302025Member_019eb09a-fa6f-7636-a55f-50c59d26b31e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_RevolvingLoansAfterSeptember302025Member_019eb09a-fa6f-7371-b647-a0ef257d6ecf" xlink:href="ebs-20260630.xsd#ebs_RevolvingLoansAfterSeptember302025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ebs_RevolvingLoansMember_019eb09a-fa6f-7764-b703-f9fafb245dba" xlink:to="loc_ebs_RevolvingLoansAfterSeptember302025Member_019eb09a-fa6f-7371-b647-a0ef257d6ecf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019eb09a-fa6f-752d-a89e-bb827e98760a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-731c-9323-c292c161efd2" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019eb09a-fa6f-752d-a89e-bb827e98760a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019eb09a-fa6f-752d-a89e-bb827e98760a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019eb09a-fa6f-752d-a89e-bb827e98760a" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019eb09a-fa6f-752d-a89e-bb827e98760a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019eb09a-fa6f-70ac-b76c-413821b6bcb5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019eb09a-fa6f-752d-a89e-bb827e98760a" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019eb09a-fa6f-70ac-b76c-413821b6bcb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019eb09a-fa6f-7d38-90f0-e00735df359e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019eb09a-fa6f-70ac-b76c-413821b6bcb5" xlink:to="loc_us-gaap_LineOfCreditMember_019eb09a-fa6f-7d38-90f0-e00735df359e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_019eb09a-fa6f-74e4-b322-b266d2ef903c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e1de2-c711-731c-9323-c292c161efd2" xlink:to="loc_us-gaap_VariableRateAxis_019eb09a-fa6f-74e4-b322-b266d2ef903c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019eb09a-fa6f-74e4-b322-b266d2ef903c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_019eb09a-fa6f-74e4-b322-b266d2ef903c" xlink:to="loc_us-gaap_VariableRateDomain_019eb09a-fa6f-74e4-b322-b266d2ef903c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019eb09a-fa6f-7f56-a7c1-f26a7edf8308" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_019eb09a-fa6f-74e4-b322-b266d2ef903c" xlink:to="loc_us-gaap_VariableRateDomain_019eb09a-fa6f-7f56-a7c1-f26a7edf8308" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_019eb09a-fa6f-7299-94fd-0b3f70afbff1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019eb09a-fa6f-7f56-a7c1-f26a7edf8308" xlink:to="loc_us-gaap_BaseRateMember_019eb09a-fa6f-7299-94fd-0b3f70afbff1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019eb09a-fa6f-7a36-a25d-d524260ec849" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019eb09a-fa6f-7f56-a7c1-f26a7edf8308" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019eb09a-fa6f-7a36-a25d-d524260ec849" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019eb09a-fa6f-7669-ae3e-a478a5d67664" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7754-872c-3fbf259d28ba" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019eb09a-fa6f-7669-ae3e-a478a5d67664" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_LineOfCreditFacilityMaximumBorrowingCapacityIncreaseLimit_019eb09a-fa6f-70b1-ad63-427ab1e83f25" xlink:href="ebs-20260630.xsd#ebs_LineOfCreditFacilityMaximumBorrowingCapacityIncreaseLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7754-872c-3fbf259d28ba" xlink:to="loc_ebs_LineOfCreditFacilityMaximumBorrowingCapacityIncreaseLimit_019eb09a-fa6f-70b1-ad63-427ab1e83f25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_LineOfCreditFacilityMaximumBorrowingCapacityDecreaseLimit_019eb09a-fa6f-77ae-91b6-6df17538f6bb" xlink:href="ebs-20260630.xsd#ebs_LineOfCreditFacilityMaximumBorrowingCapacityDecreaseLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7754-872c-3fbf259d28ba" xlink:to="loc_ebs_LineOfCreditFacilityMaximumBorrowingCapacityDecreaseLimit_019eb09a-fa6f-77ae-91b6-6df17538f6bb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019eb09a-fa6f-7a00-babf-c89fb2ab9b4d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7754-872c-3fbf259d28ba" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019eb09a-fa6f-7a00-babf-c89fb2ab9b4d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentVariableInterestRateFloor_019eb09a-fa6f-7bbf-9d49-77f379318102" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentVariableInterestRateFloor"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7754-872c-3fbf259d28ba" xlink:to="loc_ebs_DebtInstrumentVariableInterestRateFloor_019eb09a-fa6f-7bbf-9d49-77f379318102" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentCovenantLeverageRatioForVariableRateReductionMaximum_019eb09a-fa6f-7d43-bd4c-c3c6a854e6d7" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentCovenantLeverageRatioForVariableRateReductionMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7754-872c-3fbf259d28ba" xlink:to="loc_ebs_DebtInstrumentCovenantLeverageRatioForVariableRateReductionMaximum_019eb09a-fa6f-7d43-bd4c-c3c6a854e6d7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019eb09a-fa6f-724c-ac73-56f32a68942e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7754-872c-3fbf259d28ba" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019eb09a-fa6f-724c-ac73-56f32a68942e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentCovenantMaturityNumberOfDaysPriorToTheMaturityDate_019eb09a-fa6f-7b72-a300-ed6f5ffa644d" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentCovenantMaturityNumberOfDaysPriorToTheMaturityDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7754-872c-3fbf259d28ba" xlink:to="loc_ebs_DebtInstrumentCovenantMaturityNumberOfDaysPriorToTheMaturityDate_019eb09a-fa6f-7b72-a300-ed6f5ffa644d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentCovenantLiquidityRequirementMinimum_019eb09a-fa6f-7b5a-b5f9-b40df74a99fb" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentCovenantLiquidityRequirementMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7754-872c-3fbf259d28ba" xlink:to="loc_ebs_DebtInstrumentCovenantLiquidityRequirementMinimum_019eb09a-fa6f-7b5a-b5f9-b40df74a99fb" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentCovenantLeverageRatioPeriod_019eb09a-fa6f-728f-8986-8f58003eeedd" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentCovenantLeverageRatioPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7754-872c-3fbf259d28ba" xlink:to="loc_ebs_DebtInstrumentCovenantLeverageRatioPeriod_019eb09a-fa6f-728f-8986-8f58003eeedd" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentCovenantConsolidatedSecuredLeverageRatioMaximum_019eb09a-fa6f-7e7b-8862-8cde4667c6ae" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentCovenantConsolidatedSecuredLeverageRatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7754-872c-3fbf259d28ba" xlink:to="loc_ebs_DebtInstrumentCovenantConsolidatedSecuredLeverageRatioMaximum_019eb09a-fa6f-7e7b-8862-8cde4667c6ae" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_DebtInstrumentCovenantFixedChargeCoverageRatioMinimum_019eb09a-fa6f-7ef8-9f67-06fff49c273e" xlink:href="ebs-20260630.xsd#ebs_DebtInstrumentCovenantFixedChargeCoverageRatioMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e1de2-c711-7754-872c-3fbf259d28ba" xlink:to="loc_ebs_DebtInstrumentCovenantFixedChargeCoverageRatioMinimum_019eb09a-fa6f-7ef8-9f67-06fff49c273e" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/StockbasedcompensationandstockholdersequityNarrativeDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#StockbasedcompensationandstockholdersequityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/StockbasedcompensationandstockholdersequityNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e1de2-c712-7ad1-8730-3f75afe0c906" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e1de2-c712-7ad1-8730-3f75afe0c906" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e1de2-c712-7b76-a273-479386566a89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e1de2-c712-7ad1-8730-3f75afe0c906" xlink:to="loc_us-gaap_AwardTypeAxis_019e1de2-c712-7b76-a273-479386566a89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e1de2-c712-7b76-a273-479386566a89_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019e1de2-c712-7b76-a273-479386566a89" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e1de2-c712-7b76-a273-479386566a89_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e1de2-c712-7464-bc68-c03d9b1978a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019e1de2-c712-7b76-a273-479386566a89" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e1de2-c712-7464-bc68-c03d9b1978a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019e1de2-c712-7e15-9d39-5fd1de7345c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e1de2-c712-7464-bc68-c03d9b1978a2" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019e1de2-c712-7e15-9d39-5fd1de7345c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019e1de2-c712-7ec7-88ed-d0e78c100337" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e1de2-c712-7464-bc68-c03d9b1978a2" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019e1de2-c712-7ec7-88ed-d0e78c100337" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_LongTermIncentiveAwardMember_019e1de2-c712-7c8f-9d46-02740793ce0b" xlink:href="ebs-20260630.xsd#ebs_LongTermIncentiveAwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e1de2-c712-7464-bc68-c03d9b1978a2" xlink:to="loc_ebs_LongTermIncentiveAwardMember_019e1de2-c712-7c8f-9d46-02740793ce0b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_PerformanceStockOptionMember_019e1de2-c712-7e40-8b93-ddba46821ce1" xlink:href="ebs-20260630.xsd#ebs_PerformanceStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e1de2-c712-7464-bc68-c03d9b1978a2" xlink:to="loc_ebs_PerformanceStockOptionMember_019e1de2-c712-7e40-8b93-ddba46821ce1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_OtherEquityAwardsMember_019e1de2-c712-7381-a2a6-5c8a06830c8a" xlink:href="ebs-20260630.xsd#ebs_OtherEquityAwardsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e1de2-c712-7464-bc68-c03d9b1978a2" xlink:to="loc_ebs_OtherEquityAwardsMember_019e1de2-c712-7381-a2a6-5c8a06830c8a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019e1de2-c712-78c4-826e-42c0cb169b02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e1de2-c712-7464-bc68-c03d9b1978a2" xlink:to="loc_us-gaap_PerformanceSharesMember_019e1de2-c712-78c4-826e-42c0cb169b02" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramAxis_019e1de2-c712-70cf-b9fc-8e26f1bd09c9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e1de2-c712-7ad1-8730-3f75afe0c906" xlink:to="loc_srt_ShareRepurchaseProgramAxis_019e1de2-c712-70cf-b9fc-8e26f1bd09c9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_019e1de2-c712-70cf-b9fc-8e26f1bd09c9_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ShareRepurchaseProgramAxis_019e1de2-c712-70cf-b9fc-8e26f1bd09c9" xlink:to="loc_srt_ShareRepurchaseProgramDomain_019e1de2-c712-70cf-b9fc-8e26f1bd09c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_019e1de2-c712-7a7c-8f39-b3bfe13fb390" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ShareRepurchaseProgramAxis_019e1de2-c712-70cf-b9fc-8e26f1bd09c9" xlink:to="loc_srt_ShareRepurchaseProgramDomain_019e1de2-c712-7a7c-8f39-b3bfe13fb390" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_A2025ShareRepurchaseProgramMember_019e1de2-c712-7f99-b95e-88ad97c7dc35" xlink:href="ebs-20260630.xsd#ebs_A2025ShareRepurchaseProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_019e1de2-c712-7a7c-8f39-b3bfe13fb390" xlink:to="loc_ebs_A2025ShareRepurchaseProgramMember_019e1de2-c712-7f99-b95e-88ad97c7dc35" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_ReauthorizedShareRepurchaseProgramMember_019e1de2-c712-7d04-b5bd-ecf5287ebd77" xlink:href="ebs-20260630.xsd#ebs_ReauthorizedShareRepurchaseProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_019e1de2-c712-7a7c-8f39-b3bfe13fb390" xlink:to="loc_ebs_ReauthorizedShareRepurchaseProgramMember_019e1de2-c712-7d04-b5bd-ecf5287ebd77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c712-74ef-9748-67f55a2f3f1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e1de2-c712-7ad1-8730-3f75afe0c906" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c712-74ef-9748-67f55a2f3f1d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c712-74ef-9748-67f55a2f3f1d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c712-74ef-9748-67f55a2f3f1d" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c712-74ef-9748-67f55a2f3f1d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c712-7bb4-b24f-c0b5942a0369" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c712-74ef-9748-67f55a2f3f1d" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c712-7bb4-b24f-c0b5942a0369" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_SeriesIWarrantsMember_019e1de2-c712-7559-8540-507349975244" xlink:href="ebs-20260630.xsd#ebs_SeriesIWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c712-7bb4-b24f-c0b5942a0369" xlink:to="loc_ebs_SeriesIWarrantsMember_019e1de2-c712-7559-8540-507349975244" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_SeriesIIWarrantsMember_019e1de2-c712-735f-b95f-c6f7713a0076" xlink:href="ebs-20260630.xsd#ebs_SeriesIIWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c712-7bb4-b24f-c0b5942a0369" xlink:to="loc_ebs_SeriesIIWarrantsMember_019e1de2-c712-735f-b95f-c6f7713a0076" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e1de2-c712-7be3-b9bd-8aeefeefddae" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e1de2-c712-7ad1-8730-3f75afe0c906" xlink:to="loc_srt_RangeAxis_019e1de2-c712-7be3-b9bd-8aeefeefddae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e1de2-c712-7be3-b9bd-8aeefeefddae_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019e1de2-c712-7be3-b9bd-8aeefeefddae" xlink:to="loc_srt_RangeMember_019e1de2-c712-7be3-b9bd-8aeefeefddae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e1de2-c712-7f0e-b468-67d1a78596be" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019e1de2-c712-7be3-b9bd-8aeefeefddae" xlink:to="loc_srt_RangeMember_019e1de2-c712-7f0e-b468-67d1a78596be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019e1de2-c712-7e2f-ba0c-b40f71e5514f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e1de2-c712-7f0e-b468-67d1a78596be" xlink:to="loc_srt_MinimumMember_019e1de2-c712-7e2f-ba0c-b40f71e5514f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e1de2-c712-7ccb-bb90-5a0fdf9004a5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e1de2-c712-7f0e-b468-67d1a78596be" xlink:to="loc_srt_MaximumMember_019e1de2-c712-7ccb-bb90-5a0fdf9004a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_019e1de2-c712-748c-bb77-105fa53cd559" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_019e1de2-c712-748c-bb77-105fa53cd559" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019e1de2-c712-79bf-8ff1-a90544a481ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019e1de2-c712-79bf-8ff1-a90544a481ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodGrantDateFairValue_019e1de2-c712-7c1c-b9f7-be516d236489" xlink:href="ebs-20260630.xsd#ebs_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_ebs_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodGrantDateFairValue_019e1de2-c712-7c1c-b9f7-be516d236489" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019e1de2-c712-7285-8767-5e058d48bcd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019e1de2-c712-7285-8767-5e058d48bcd2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfVestingIncrements_019e1de2-c712-780e-ae26-31cbcc2f840a" xlink:href="ebs-20260630.xsd#ebs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfVestingIncrements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_ebs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfVestingIncrements_019e1de2-c712-780e-ae26-31cbcc2f840a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedNumberOfShares_019e1de2-c712-7d7a-8ca3-20b9a5f3b8d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedNumberOfShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedNumberOfShares_019e1de2-c712-7d7a-8ca3-20b9a5f3b8d0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019e1de2-c712-75c2-b475-c408564e5d95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019e1de2-c712-75c2-b475-c408564e5d95" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019e1de2-c712-7b65-b4a9-274c2757c07f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019e1de2-c712-7b65-b4a9-274c2757c07f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareRepurchaseProgramExciseTax_019e5e8e-a57c-7ccd-822b-41851a8c392d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareRepurchaseProgramExciseTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_us-gaap_ShareRepurchaseProgramExciseTax_019e5e8e-a57c-7ccd-822b-41851a8c392d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_TreasuryStockValueAcquiredCostMethodIncludingCommissionsAndExciseTax_019e1de2-c712-7eaa-8d46-ee0ef474472a" xlink:href="ebs-20260630.xsd#ebs_TreasuryStockValueAcquiredCostMethodIncludingCommissionsAndExciseTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_ebs_TreasuryStockValueAcquiredCostMethodIncludingCommissionsAndExciseTax_019e1de2-c712-7eaa-8d46-ee0ef474472a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_019e1de2-c712-7ae7-a93d-c0d1ea423e55" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_019e1de2-c712-7ae7-a93d-c0d1ea423e55" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockAcquiredAverageCostPerShare_019e1de2-c712-7274-8209-fbeaff179787" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockAcquiredAverageCostPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_us-gaap_TreasuryStockAcquiredAverageCostPerShare_019e1de2-c712-7274-8209-fbeaff179787" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_019e1de2-c712-75ba-b298-174855deb13f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_019e1de2-c712-75ba-b298-174855deb13f" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019e1de2-c712-7544-97a5-ba326053a213" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019e1de2-c712-7544-97a5-ba326053a213" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_WarrantLiabilitiesFairValueDisclosure_019e1de2-c712-73f5-839f-b746748ec1e5" xlink:href="ebs-20260630.xsd#ebs_WarrantLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-74a5-9b93-cdc164a354e8" xlink:to="loc_ebs_WarrantLiabilitiesFairValueDisclosure_019e1de2-c712-73f5-839f-b746748ec1e5" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/StockbasedcompensationandstockholdersequityScheduleofStockbasedCompensationExpenseDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#StockbasedcompensationandstockholdersequityScheduleofStockbasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/StockbasedcompensationandstockholdersequityScheduleofStockbasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-7bc4-b5ae-91bffa323870" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e1de2-c712-73b3-8637-00153a53f0c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-7bc4-b5ae-91bffa323870" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e1de2-c712-73b3-8637-00153a53f0c8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019e1de2-c712-7853-a285-e9ab5ad91c15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e1de2-c712-73b3-8637-00153a53f0c8" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019e1de2-c712-7853-a285-e9ab5ad91c15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e1de2-c712-7d6e-abea-b65772be5df1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-7bc4-b5ae-91bffa323870" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e1de2-c712-7d6e-abea-b65772be5df1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/StockbasedcompensationandstockholdersequityScheduleofStockbasedCompensationExpenseDetails_1" xlink:type="simple" xlink:href="ebs-20260630.xsd#StockbasedcompensationandstockholdersequityScheduleofStockbasedCompensationExpenseDetails_1"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/StockbasedcompensationandstockholdersequityScheduleofStockbasedCompensationExpenseDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-7bc4-b5ae-91bffa323870" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e1de2-c712-73b3-8637-00153a53f0c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-7bc4-b5ae-91bffa323870" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e1de2-c712-73b3-8637-00153a53f0c8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e1de2-c712-7d6e-abea-b65772be5df1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e1de2-c712-7bc4-b5ae-91bffa323870" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e1de2-c712-7d6e-abea-b65772be5df1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/StockbasedcompensationandstockholdersequityScheduleofStockholdersEquityNoteWarrantsorRightsDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#StockbasedcompensationandstockholdersequityScheduleofStockholdersEquityNoteWarrantsorRightsDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/StockbasedcompensationandstockholdersequityScheduleofStockholdersEquityNoteWarrantsorRightsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_019e1de2-c712-7952-8675-8f654b60b74d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightTable_019e1de2-c712-77a7-be10-dd9b29dff1e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019e1de2-c712-7952-8675-8f654b60b74d" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_019e1de2-c712-77a7-be10-dd9b29dff1e6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c712-70b5-a2f4-ad55f65a4666" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019e1de2-c712-77a7-be10-dd9b29dff1e6" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c712-70b5-a2f4-ad55f65a4666" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c712-70b5-a2f4-ad55f65a4666_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c712-70b5-a2f4-ad55f65a4666" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c712-70b5-a2f4-ad55f65a4666_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c712-73b2-81c7-086c53be74bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019e1de2-c712-70b5-a2f4-ad55f65a4666" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c712-73b2-81c7-086c53be74bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_A2024WarrantsMember_019e1de2-c712-7c62-bf36-d2e7519af3e1" xlink:href="ebs-20260630.xsd#ebs_A2024WarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019e1de2-c712-73b2-81c7-086c53be74bf" xlink:to="loc_ebs_A2024WarrantsMember_019e1de2-c712-7c62-bf36-d2e7519af3e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e1de2-c712-732a-bed1-c3d9dd31a756" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019e1de2-c712-77a7-be10-dd9b29dff1e6" xlink:to="loc_srt_RangeAxis_019e1de2-c712-732a-bed1-c3d9dd31a756" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e1de2-c712-732a-bed1-c3d9dd31a756_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019e1de2-c712-732a-bed1-c3d9dd31a756" xlink:to="loc_srt_RangeMember_019e1de2-c712-732a-bed1-c3d9dd31a756_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e1de2-c712-72b9-a34b-fb5b341283cb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019e1de2-c712-732a-bed1-c3d9dd31a756" xlink:to="loc_srt_RangeMember_019e1de2-c712-72b9-a34b-fb5b341283cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019e1de2-c712-7276-a6f3-f43a475340b6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e1de2-c712-72b9-a34b-fb5b341283cb" xlink:to="loc_srt_MinimumMember_019e1de2-c712-7276-a6f3-f43a475340b6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e1de2-c712-7ca1-862c-d8f7c75bf25f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e1de2-c712-72b9-a34b-fb5b341283cb" xlink:to="loc_srt_MaximumMember_019e1de2-c712-7ca1-862c-d8f7c75bf25f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019e1de2-c712-7907-9b9f-e8638e3e7fe3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019e1de2-c712-7952-8675-8f654b60b74d" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019e1de2-c712-7907-9b9f-e8638e3e7fe3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019e1de2-c712-7469-809b-f0d43c8c3798" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019e1de2-c712-7952-8675-8f654b60b74d" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019e1de2-c712-7469-809b-f0d43c8c3798" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/RevenuerecognitionScheduleofDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#RevenuerecognitionScheduleofDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/RevenuerecognitionScheduleofDisaggregationofRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-7afd-8bee-beacd6b3ef49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019e1de2-c712-7fa0-abb7-7c8dda11aa21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-7afd-8bee-beacd6b3ef49" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e1de2-c712-7fa0-abb7-7c8dda11aa21" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019e1de2-c712-7f57-a769-cd23191d4bed" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019e1de2-c712-7fa0-abb7-7c8dda11aa21" xlink:to="loc_srt_MajorCustomersAxis_019e1de2-c712-7f57-a769-cd23191d4bed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019e1de2-c712-7f57-a769-cd23191d4bed_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019e1de2-c712-7f57-a769-cd23191d4bed" xlink:to="loc_srt_NameOfMajorCustomerDomain_019e1de2-c712-7f57-a769-cd23191d4bed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019e1de2-c712-7e86-9968-ac3435c7bd31" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019e1de2-c712-7f57-a769-cd23191d4bed" xlink:to="loc_srt_NameOfMajorCustomerDomain_019e1de2-c712-7e86-9968-ac3435c7bd31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_UnitedStatesGovernmentMember_019e1de2-c712-721a-9c2a-3b390ef4f9ba" xlink:href="ebs-20260630.xsd#ebs_UnitedStatesGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019e1de2-c712-7e86-9968-ac3435c7bd31" xlink:to="loc_ebs_UnitedStatesGovernmentMember_019e1de2-c712-721a-9c2a-3b390ef4f9ba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_NonUnitedStatesGovernmentMember_019e1de2-c712-7d27-b951-a65862701a59" xlink:href="ebs-20260630.xsd#ebs_NonUnitedStatesGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019e1de2-c712-7e86-9968-ac3435c7bd31" xlink:to="loc_ebs_NonUnitedStatesGovernmentMember_019e1de2-c712-7d27-b951-a65862701a59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019e1de2-c712-7ee7-b860-b4adf1cf658a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019e1de2-c712-7fa0-abb7-7c8dda11aa21" xlink:to="loc_srt_ProductOrServiceAxis_019e1de2-c712-7ee7-b860-b4adf1cf658a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e1de2-c712-7ee7-b860-b4adf1cf658a_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019e1de2-c712-7ee7-b860-b4adf1cf658a" xlink:to="loc_srt_ProductsAndServicesDomain_019e1de2-c712-7ee7-b860-b4adf1cf658a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e1de2-c712-75d9-a419-28535aaa38bc" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019e1de2-c712-7ee7-b860-b4adf1cf658a" xlink:to="loc_srt_ProductsAndServicesDomain_019e1de2-c712-75d9-a419-28535aaa38bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_CommercialProductMember_019e1de2-c712-7a38-ad37-5614816acb8b" xlink:href="ebs-20260630.xsd#ebs_CommercialProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e1de2-c712-75d9-a419-28535aaa38bc" xlink:to="loc_ebs_CommercialProductMember_019e1de2-c712-7a38-ad37-5614816acb8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_MedicalCountermeasuresMCMProductMember_019e1de2-c712-7000-9eb0-1c2fadeee4f7" xlink:href="ebs-20260630.xsd#ebs_MedicalCountermeasuresMCMProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e1de2-c712-75d9-a419-28535aaa38bc" xlink:to="loc_ebs_MedicalCountermeasuresMCMProductMember_019e1de2-c712-7000-9eb0-1c2fadeee4f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_AllOtherRevenueMember_019e1de2-c712-7b02-b7e4-73d4e7f4fac9" xlink:href="ebs-20260630.xsd#ebs_AllOtherRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e1de2-c712-75d9-a419-28535aaa38bc" xlink:to="loc_ebs_AllOtherRevenueMember_019e1de2-c712-7b02-b7e4-73d4e7f4fac9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e1de2-c712-7283-836b-258173da992b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-7afd-8bee-beacd6b3ef49" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e1de2-c712-7283-836b-258173da992b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/RevenuerecognitionNarrativeDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#RevenuerecognitionNarrativeDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/RevenuerecognitionNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-762e-8824-9895e923cad9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019e1de2-c712-703e-96a6-6094a6b292fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-762e-8824-9895e923cad9" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e1de2-c712-703e-96a6-6094a6b292fd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019e1de2-c712-7d36-afc8-656788469d3b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019e1de2-c712-703e-96a6-6094a6b292fd" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019e1de2-c712-7d36-afc8-656788469d3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_019e1de2-c712-7367-a0e5-82c4c2573c43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-762e-8824-9895e923cad9" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_019e1de2-c712-7367-a0e5-82c4c2573c43" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019e1de2-c712-70bd-87d9-c9e2e3c1a0de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-762e-8824-9895e923cad9" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019e1de2-c712-70bd-87d9-c9e2e3c1a0de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetNoncurrent_019e1de2-c712-75f8-9d6c-7ef410012af7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetNetNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-762e-8824-9895e923cad9" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetNoncurrent_019e1de2-c712-75f8-9d6c-7ef410012af7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019e1de2-c712-79d1-b2a5-d63f71963f1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-762e-8824-9895e923cad9" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019e1de2-c712-79d1-b2a5-d63f71963f1a" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/RevenuerecognitionNarrativeDetails_1" xlink:type="simple" xlink:href="ebs-20260630.xsd#RevenuerecognitionNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/RevenuerecognitionNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-762e-8824-9895e923cad9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019e1de2-c712-703e-96a6-6094a6b292fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-762e-8824-9895e923cad9" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e1de2-c712-703e-96a6-6094a6b292fd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_019e1de2-c712-7367-a0e5-82c4c2573c43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-762e-8824-9895e923cad9" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_019e1de2-c712-7367-a0e5-82c4c2573c43" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019e1de2-c712-70bd-87d9-c9e2e3c1a0de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-762e-8824-9895e923cad9" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019e1de2-c712-70bd-87d9-c9e2e3c1a0de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetNoncurrent_019e1de2-c712-75f8-9d6c-7ef410012af7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetNetNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-762e-8824-9895e923cad9" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetNoncurrent_019e1de2-c712-75f8-9d6c-7ef410012af7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019e1de2-c712-79d1-b2a5-d63f71963f1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e1de2-c712-762e-8824-9895e923cad9" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019e1de2-c712-79d1-b2a5-d63f71963f1a" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/IncometaxesDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#IncometaxesDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/IncometaxesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019e1de2-c712-7e48-941d-f997083db7d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019e1de2-c712-787a-a938-43a23427b52d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019e1de2-c712-7e48-941d-f997083db7d7" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019e1de2-c712-787a-a938-43a23427b52d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019e1de2-c712-7096-8f22-e97ac6839c3c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019e1de2-c712-787a-a938-43a23427b52d" xlink:to="loc_srt_StatementScenarioAxis_019e1de2-c712-7096-8f22-e97ac6839c3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019e1de2-c712-7096-8f22-e97ac6839c3c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019e1de2-c712-7096-8f22-e97ac6839c3c" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019e1de2-c712-7096-8f22-e97ac6839c3c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019e1de2-c712-7832-a70a-2be1e565c5bb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019e1de2-c712-7096-8f22-e97ac6839c3c" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019e1de2-c712-7832-a70a-2be1e565c5bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019e1de2-c712-779b-bca4-1e6d7d98176a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019e1de2-c712-7832-a70a-2be1e565c5bb" xlink:to="loc_srt_ScenarioForecastMember_019e1de2-c712-779b-bca4-1e6d7d98176a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019e1de2-c712-7810-bd6e-1e05e0f019f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019e1de2-c712-7e48-941d-f997083db7d7" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019e1de2-c712-7810-bd6e-1e05e0f019f1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/SegmentinformationScheduleofReconciliationofOperatingProfitLossfromSegmentstoConsolidatedDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#SegmentinformationScheduleofReconciliationofOperatingProfitLossfromSegmentstoConsolidatedDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/SegmentinformationScheduleofReconciliationofOperatingProfitLossfromSegmentstoConsolidatedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019e1de2-c712-704d-8dfd-b2a1ff789dfd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e1de2-c712-7da6-99f0-25f52443bd17" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e1de2-c712-704d-8dfd-b2a1ff789dfd" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e1de2-c712-7da6-99f0-25f52443bd17" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019e1de2-c712-70a6-828f-21eda91c9497" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e1de2-c712-7da6-99f0-25f52443bd17" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019e1de2-c712-70a6-828f-21eda91c9497" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e1de2-c712-70a6-828f-21eda91c9497_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019e1de2-c712-70a6-828f-21eda91c9497" xlink:to="loc_us-gaap_SegmentDomain_019e1de2-c712-70a6-828f-21eda91c9497_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e1de2-c712-77a0-bd42-a71945435f9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019e1de2-c712-70a6-828f-21eda91c9497" xlink:to="loc_us-gaap_SegmentDomain_019e1de2-c712-77a0-bd42-a71945435f9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_CommercialProductsSegmentMember_019e1de2-c712-739a-b0b1-b07767a98dc0" xlink:href="ebs-20260630.xsd#ebs_CommercialProductsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e1de2-c712-77a0-bd42-a71945435f9f" xlink:to="loc_ebs_CommercialProductsSegmentMember_019e1de2-c712-739a-b0b1-b07767a98dc0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_MCMProductsSegmentMember_019e1de2-c712-7cc3-aac9-6a49d00f41cf" xlink:href="ebs-20260630.xsd#ebs_MCMProductsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e1de2-c712-77a0-bd42-a71945435f9f" xlink:to="loc_ebs_MCMProductsSegmentMember_019e1de2-c712-7cc3-aac9-6a49d00f41cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019e1de2-c712-7a38-b3b4-9fa5f1c474dd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e1de2-c712-7da6-99f0-25f52443bd17" xlink:to="loc_srt_ConsolidationItemsAxis_019e1de2-c712-7a38-b3b4-9fa5f1c474dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019e1de2-c712-7a38-b3b4-9fa5f1c474dd_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019e1de2-c712-7a38-b3b4-9fa5f1c474dd" xlink:to="loc_srt_ConsolidationItemsDomain_019e1de2-c712-7a38-b3b4-9fa5f1c474dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019e1de2-c712-7cda-9ca6-b9764344a80c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019e1de2-c712-7a38-b3b4-9fa5f1c474dd" xlink:to="loc_srt_ConsolidationItemsDomain_019e1de2-c712-7cda-9ca6-b9764344a80c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019e1de2-c712-7ac6-a696-d8567956cb08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019e1de2-c712-7cda-9ca6-b9764344a80c" xlink:to="loc_us-gaap_OperatingSegmentsMember_019e1de2-c712-7ac6-a696-d8567956cb08" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_019e1de2-c712-718a-bc0b-788c078af7b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MaterialReconcilingItemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019e1de2-c712-7cda-9ca6-b9764344a80c" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_019e1de2-c712-718a-bc0b-788c078af7b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_019e1de2-c712-73bc-98d3-0bb0575f9775" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e1de2-c712-704d-8dfd-b2a1ff789dfd" xlink:to="loc_us-gaap_RevenuesAbstract_019e1de2-c712-73bc-98d3-0bb0575f9775" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e1de2-c712-7e69-8d5e-b74adab7e177" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019e1de2-c712-73bc-98d3-0bb0575f9775" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e1de2-c712-7e69-8d5e-b74adab7e177" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_019e1de2-c712-7c0f-a119-9fa2f6786c9c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSoldAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e1de2-c712-704d-8dfd-b2a1ff789dfd" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_019e1de2-c712-7c0f-a119-9fa2f6786c9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019e1de2-c712-780a-8950-4e4c7f101c1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_019e1de2-c712-7c0f-a119-9fa2f6786c9c" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019e1de2-c712-780a-8950-4e4c7f101c1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_AdjustedGrossMargin_019e1de2-c712-72fb-8b9e-ec8a9b9f8579" xlink:href="ebs-20260630.xsd#ebs_AdjustedGrossMargin"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e1de2-c712-704d-8dfd-b2a1ff789dfd" xlink:to="loc_ebs_AdjustedGrossMargin_019e1de2-c712-72fb-8b9e-ec8a9b9f8579" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e1de2-c712-704d-8dfd-b2a1ff789dfd" xlink:to="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019e1de2-c712-792e-819d-19f3ab7c2d65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019e1de2-c712-792e-819d-19f3ab7c2d65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019e1de2-c712-7b05-be55-15d3c8da203a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019e1de2-c712-7b05-be55-15d3c8da203a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_019ec8fe-fb58-7fee-acaa-078662bd3437" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:to="loc_us-gaap_RestructuringCharges_019ec8fe-fb58-7fee-acaa-078662bd3437" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_InventoryStepUp_019e1de2-c712-74f7-ad7e-7509fc7460ad" xlink:href="ebs-20260630.xsd#ebs_InventoryStepUp"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:to="loc_ebs_InventoryStepUp_019e1de2-c712-74f7-ad7e-7509fc7460ad" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e1de2-c712-727c-926e-18174d4a5adb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e1de2-c712-727c-926e-18174d4a5adb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_019fa469-3324-7ef7-80c8-daecc66c4492" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_019fa469-3324-7ef7-80c8-daecc66c4492" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019e1de2-c712-7e4c-800f-ab6a1b0123fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019e1de2-c712-7e4c-800f-ab6a1b0123fe" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019e1de2-c712-7c2a-b130-2450f0f72bfb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019e1de2-c712-7c2a-b130-2450f0f72bfb" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019e1de2-c712-728e-93db-ba8023fc8807" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019e1de2-c712-728e-93db-ba8023fc8807" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_019e1de2-c712-7d81-8290-8cdf7ee1f48a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:to="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_019e1de2-c712-7d81-8290-8cdf7ee1f48a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019fa469-e10e-7cc8-8d39-2e5cbf74a438" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019fa469-e10e-7cc8-8d39-2e5cbf74a438" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019e1de2-c712-7b76-8152-4c5daa273985" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019e1de2-c712-7b76-8152-4c5daa273985" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019e1de2-c712-7f9f-b291-c339cfa38ee1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingOtherSignificantReconcilingItemConsolidatedAbstract_019e1de2-c712-7c13-bcdf-e99b2fd61f1a" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019e1de2-c712-7f9f-b291-c339cfa38ee1" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/SegmentinformationScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#SegmentinformationScheduleofSegmentReportingInformationbySegmentDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/SegmentinformationScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019e1de2-c712-742b-87d7-997323b56a65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e1de2-c712-7754-8a34-c3e7fa714c6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e1de2-c712-742b-87d7-997323b56a65" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e1de2-c712-7754-8a34-c3e7fa714c6b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019e1de2-c712-7c23-b419-d25b809c3844" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e1de2-c712-7754-8a34-c3e7fa714c6b" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019e1de2-c712-7c23-b419-d25b809c3844" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e1de2-c712-7c23-b419-d25b809c3844_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019e1de2-c712-7c23-b419-d25b809c3844" xlink:to="loc_us-gaap_SegmentDomain_019e1de2-c712-7c23-b419-d25b809c3844_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e1de2-c712-7cc6-9d2f-cd59909f4135" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019e1de2-c712-7c23-b419-d25b809c3844" xlink:to="loc_us-gaap_SegmentDomain_019e1de2-c712-7cc6-9d2f-cd59909f4135" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_MCMProductsSegmentMember_019e1de2-c712-7993-bb74-6cdc6b6b9ad4" xlink:href="ebs-20260630.xsd#ebs_MCMProductsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e1de2-c712-7cc6-9d2f-cd59909f4135" xlink:to="loc_ebs_MCMProductsSegmentMember_019e1de2-c712-7993-bb74-6cdc6b6b9ad4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllOtherSegmentsMember_019e1de2-c712-7577-b95c-8493333ef55c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllOtherSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e1de2-c712-7cc6-9d2f-cd59909f4135" xlink:to="loc_us-gaap_AllOtherSegmentsMember_019e1de2-c712-7577-b95c-8493333ef55c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019e1de2-c712-7b20-bf25-a7a134cafb9a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e1de2-c712-7754-8a34-c3e7fa714c6b" xlink:to="loc_srt_ConsolidationItemsAxis_019e1de2-c712-7b20-bf25-a7a134cafb9a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019e1de2-c712-7b20-bf25-a7a134cafb9a_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019e1de2-c712-7b20-bf25-a7a134cafb9a" xlink:to="loc_srt_ConsolidationItemsDomain_019e1de2-c712-7b20-bf25-a7a134cafb9a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019e1de2-c712-7db9-bd1d-cd4d89f653b7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019e1de2-c712-7b20-bf25-a7a134cafb9a" xlink:to="loc_srt_ConsolidationItemsDomain_019e1de2-c712-7db9-bd1d-cd4d89f653b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019e1de2-c712-7b60-bb7e-ebf9ecf12012" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019e1de2-c712-7db9-bd1d-cd4d89f653b7" xlink:to="loc_us-gaap_OperatingSegmentsMember_019e1de2-c712-7b60-bb7e-ebf9ecf12012" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_019e1de2-c712-7535-8d9d-7a94e024dd7a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MaterialReconcilingItemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019e1de2-c712-7db9-bd1d-cd4d89f653b7" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_019e1de2-c712-7535-8d9d-7a94e024dd7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAbstract_019e1de2-c712-7856-ac26-1b8d1c3fec39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e1de2-c712-742b-87d7-997323b56a65" xlink:to="loc_us-gaap_DepreciationAbstract_019e1de2-c712-7856-ac26-1b8d1c3fec39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_019e1de2-c712-7cf8-a77c-72d91b92f11a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DepreciationAbstract_019e1de2-c712-7856-ac26-1b8d1c3fec39" xlink:to="loc_us-gaap_Depreciation_019e1de2-c712-7cf8-a77c-72d91b92f11a" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://emergentbiosolutions.com/role/SubsequenteventsDetails" xlink:type="simple" xlink:href="ebs-20260630.xsd#SubsequenteventsDetails"/>
  <link:definitionLink xlink:role="http://emergentbiosolutions.com/role/SubsequenteventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_019e1de2-c712-7359-a3fd-902ed6966523" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_019e1de2-c712-7044-95e6-966b31d54bd5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_019e1de2-c712-7359-a3fd-902ed6966523" xlink:to="loc_us-gaap_SubsequentEventTable_019e1de2-c712-7044-95e6-966b31d54bd5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019fb708-d17b-7187-a7ab-528875d7e761" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019e1de2-c712-7044-95e6-966b31d54bd5" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019fb708-d17b-7187-a7ab-528875d7e761" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019fb708-d17b-7187-a7ab-528875d7e761_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019fb708-d17b-7187-a7ab-528875d7e761" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019fb708-d17b-7187-a7ab-528875d7e761_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019fb708-d17b-75c0-9e32-81c2d0b5b7d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019fb708-d17b-7187-a7ab-528875d7e761" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019fb708-d17b-75c0-9e32-81c2d0b5b7d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019fb708-e5aa-7c4e-908a-a34575666a2b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019fb708-d17b-75c0-9e32-81c2d0b5b7d8" xlink:to="loc_us-gaap_SubsequentEventMember_019fb708-e5aa-7c4e-908a-a34575666a2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_019fb705-b6ff-7dd5-a5d6-61214d68fda2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019e1de2-c712-7044-95e6-966b31d54bd5" xlink:to="loc_us-gaap_RestructuringPlanAxis_019fb705-b6ff-7dd5-a5d6-61214d68fda2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019fb705-b6ff-7dd5-a5d6-61214d68fda2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_019fb705-b6ff-7dd5-a5d6-61214d68fda2" xlink:to="loc_us-gaap_RestructuringPlanDomain_019fb705-b6ff-7dd5-a5d6-61214d68fda2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019fb705-b6ff-78c1-aba7-2b8d350d62f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_019fb705-b6ff-7dd5-a5d6-61214d68fda2" xlink:to="loc_us-gaap_RestructuringPlanDomain_019fb705-b6ff-78c1-aba7-2b8d350d62f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_OrganizationalRestructuringPlanAugust2026Member_019fb705-b6ff-73e9-861a-20b52f1edc8d" xlink:href="ebs-20260630.xsd#ebs_OrganizationalRestructuringPlanAugust2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019fb705-b6ff-78c1-aba7-2b8d350d62f2" xlink:to="loc_ebs_OrganizationalRestructuringPlanAugust2026Member_019fb705-b6ff-73e9-861a-20b52f1edc8d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fb704-b6d2-7565-ab6f-68a6a7f9a253" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019e1de2-c712-7044-95e6-966b31d54bd5" xlink:to="loc_srt_RangeAxis_019fb704-b6d2-7565-ab6f-68a6a7f9a253" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fb704-b6d2-7565-ab6f-68a6a7f9a253_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fb704-b6d2-7565-ab6f-68a6a7f9a253" xlink:to="loc_srt_RangeMember_019fb704-b6d2-7565-ab6f-68a6a7f9a253_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fb704-b6d2-704f-b273-c90dacc71c94" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fb704-b6d2-7565-ab6f-68a6a7f9a253" xlink:to="loc_srt_RangeMember_019fb704-b6d2-704f-b273-c90dacc71c94" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fb705-05d1-7f89-886e-6cd77a23c4ac" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fb704-b6d2-704f-b273-c90dacc71c94" xlink:to="loc_srt_MinimumMember_019fb705-05d1-7f89-886e-6cd77a23c4ac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fb705-2067-7b73-bc1c-a063812c7929" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fb704-b6d2-704f-b273-c90dacc71c94" xlink:to="loc_srt_MaximumMember_019fb705-2067-7b73-bc1c-a063812c7929" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminated_019fcfa8-3e51-7698-8acf-5076a929be3a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019e1de2-c712-7359-a3fd-902ed6966523" xlink:to="loc_us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminated_019fcfa8-3e51-7698-8acf-5076a929be3a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_RestructuringAndRelatedCostNumberOfVacantPositionsEliminated_019fd248-2d9c-79dc-b1f0-adac2db2d893" xlink:href="ebs-20260630.xsd#ebs_RestructuringAndRelatedCostNumberOfVacantPositionsEliminated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019e1de2-c712-7359-a3fd-902ed6966523" xlink:to="loc_ebs_RestructuringAndRelatedCostNumberOfVacantPositionsEliminated_019fd248-2d9c-79dc-b1f0-adac2db2d893" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_019fb705-b6ff-70c1-9f64-86eb110a3c6c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringAndRelatedCostExpectedCost1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019e1de2-c712-7359-a3fd-902ed6966523" xlink:to="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_019fb705-b6ff-70c1-9f64-86eb110a3c6c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ebs_RestructuringAndRelatedCostExpectedAnnualizedSavings_019fd24a-6f34-7138-a71e-d8d2407e693e" xlink:href="ebs-20260630.xsd#ebs_RestructuringAndRelatedCostExpectedAnnualizedSavings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019e1de2-c712-7359-a3fd-902ed6966523" xlink:to="loc_ebs_RestructuringAndRelatedCostExpectedAnnualizedSavings_019fd24a-6f34-7138-a71e-d8d2407e693e" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/srt/role/srt-eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-roles-2026.xsd#eedm1"/>
  <link:definitionLink xlink:role="http://fasb.org/srt/role/srt-eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_us-gaap_OtherAssetsNoncurrent" xlink:type="arc" order="101"/>
  </link:definitionLink>
</link:linkbase>
