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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:e14fd36f-ae74-41fd-b717-b3e16abf8a36,g:3306037b-8ccc-4622-8c50-23e459de8bcc-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.firstmerchants.com/role/DocumentandEntityInformationDocument" xlink:type="simple" xlink:href="frme-20250130.xsd#DocumentandEntityInformationDocument"/>
  <link:definitionLink xlink:role="http://www.firstmerchants.com/role/DocumentandEntityInformationDocument" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityListingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityListingsTable_87282796-6e37-461f-b287-ab2e5b977589" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityListingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_EntityListingsTable_87282796-6e37-461f-b287-ab2e5b977589" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_b3a4ebcf-fa91-4d33-8fa8-ac206814ec35" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntityListingsTable_87282796-6e37-461f-b287-ab2e5b977589" xlink:to="loc_us-gaap_StatementClassOfStockAxis_b3a4ebcf-fa91-4d33-8fa8-ac206814ec35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_b3a4ebcf-fa91-4d33-8fa8-ac206814ec35_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_b3a4ebcf-fa91-4d33-8fa8-ac206814ec35" xlink:to="loc_us-gaap_ClassOfStockDomain_b3a4ebcf-fa91-4d33-8fa8-ac206814ec35_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_5f80275f-d388-4c9b-bb48-655e0c326625" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_b3a4ebcf-fa91-4d33-8fa8-ac206814ec35" xlink:to="loc_us-gaap_ClassOfStockDomain_5f80275f-d388-4c9b-bb48-655e0c326625" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_761d940b-bd4e-4bd9-8662-f4f16845c8b4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_5f80275f-d388-4c9b-bb48-655e0c326625" xlink:to="loc_us-gaap_CommonStockMember_761d940b-bd4e-4bd9-8662-f4f16845c8b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_frme_DepositarySharesMember_478154d8-bc79-470d-8636-cbd1475fe1ab" xlink:href="frme-20250130.xsd#frme_DepositarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_5f80275f-d388-4c9b-bb48-655e0c326625" xlink:to="loc_frme_DepositarySharesMember_478154d8-bc79-470d-8636-cbd1475fe1ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_ea230a4d-0422-4cee-b9d4-a83d365eba89" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_DocumentType_ea230a4d-0422-4cee-b9d4-a83d365eba89" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_62bd56df-3ee6-4bf4-b177-73610a98d6cd" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_DocumentPeriodEndDate_62bd56df-3ee6-4bf4-b177-73610a98d6cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_18754936-2446-40b5-9e2f-ef83cd39a07f" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_EntityRegistrantName_18754936-2446-40b5-9e2f-ef83cd39a07f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_803505ff-31c9-481b-bad9-c6abd026bdc4" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_EntityIncorporationStateCountryCode_803505ff-31c9-481b-bad9-c6abd026bdc4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_5b2738d9-7096-4081-a7ef-f475c2033461" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_EntityFileNumber_5b2738d9-7096-4081-a7ef-f475c2033461" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_faf601b9-d14e-478e-84a1-5969400a7979" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_EntityTaxIdentificationNumber_faf601b9-d14e-478e-84a1-5969400a7979" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_b59e2b57-272a-405b-9888-88ec5f57e85f" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_EntityAddressAddressLine1_b59e2b57-272a-405b-9888-88ec5f57e85f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_e9b97ae3-f434-4cd7-95b5-818ddb886e70" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_EntityAddressAddressLine2_e9b97ae3-f434-4cd7-95b5-818ddb886e70" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_e183c91e-8eb4-415b-a0f7-2b1d5ea98fcc" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_EntityAddressCityOrTown_e183c91e-8eb4-415b-a0f7-2b1d5ea98fcc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_7f1dd686-705a-4145-b385-c62c4223068d" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_EntityAddressStateOrProvince_7f1dd686-705a-4145-b385-c62c4223068d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_c116e9ab-8185-4f03-aa58-f1910707a6c7" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_EntityAddressPostalZipCode_c116e9ab-8185-4f03-aa58-f1910707a6c7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_20169acd-49a1-4be6-9582-641d05e58ea8" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_CityAreaCode_20169acd-49a1-4be6-9582-641d05e58ea8" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_0e2032aa-5250-4b92-b05e-dbb87a9f463a" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_LocalPhoneNumber_0e2032aa-5250-4b92-b05e-dbb87a9f463a" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_5269771d-fb9c-4a3b-92e0-667c098d6dfb" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_Security12bTitle_5269771d-fb9c-4a3b-92e0-667c098d6dfb" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_be6c1514-6af2-489f-989a-ad13fc94e54e" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_TradingSymbol_be6c1514-6af2-489f-989a-ad13fc94e54e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_cc39ec83-3573-4cf3-9cc8-b8b12e96823e" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_SecurityExchangeName_cc39ec83-3573-4cf3-9cc8-b8b12e96823e" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_6c360444-53c1-40a8-8930-3919d6da8f14" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_WrittenCommunications_6c360444-53c1-40a8-8930-3919d6da8f14" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_e5592ffe-32d4-4446-b29d-1a79e45977b6" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_SolicitingMaterial_e5592ffe-32d4-4446-b29d-1a79e45977b6" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_e389d02f-6dcd-4be1-9b88-e7510696ee61" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_PreCommencementTenderOffer_e389d02f-6dcd-4be1-9b88-e7510696ee61" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_3eba10ce-e639-41ba-b83b-0a4caf713c2f" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_3eba10ce-e639-41ba-b83b-0a4caf713c2f" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_eac3a766-e406-42f4-b2f9-41a0fd9092cc" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_EntityEmergingGrowthCompany_eac3a766-e406-42f4-b2f9-41a0fd9092cc" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_4369ebca-8481-4911-bc54-66f0c3c4429d" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_EntityCentralIndexKey_4369ebca-8481-4911-bc54-66f0c3c4429d" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_2e9446bc-f26a-48df-b461-131f4229f5da" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_b7ee3b9e-3964-4024-b701-352a948e59dd" xlink:to="loc_dei_AmendmentFlag_2e9446bc-f26a-48df-b461-131f4229f5da" xlink:type="arc" order="22"/>
  </link:definitionLink>
</link:linkbase>
