content: <?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:com="http://www.sec.gov/edgar/common">
    <headerData>
      <submissionType>144</submissionType>
      <filerInfo>
        <filer>
          <filerCredentials>
            <cik>0001222374</cik>
            <ccc>XXXXXXXX</ccc>
          </filerCredentials>
        </filer>
        <liveTestFlag>LIVE</liveTestFlag>
  
  
  
      </filerInfo>
    </headerData>
    <formData>
      <issuerInfo>
        <issuerCik>0000354190</issuerCik>
        <issuerName>Arthur J. Gallagher &amp; Co.</issuerName>
        <secFileNumber>001-09761</secFileNumber>
        <issuerAddress>
          <com:street1>2850 GOLF ROAD</com:street1>
          <com:city>ROLLING MEADOWS</com:city>
          <com:stateOrCountry>IL</com:stateOrCountry>
          <com:zipCode>60008-4050</com:zipCode>
        </issuerAddress>
        <issuerContactPhone>630-773-3800</issuerContactPhone>
        <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>HOWELL DOUGLAS K</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
        <relationshipsToIssuer>
          <relationshipToIssuer>Officer</relationshipToIssuer>
        </relationshipsToIssuer>
      </issuerInfo>
      <securitiesInformation>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <brokerOrMarketmakerDetails>
          <name>Fidelity Brokerage Services LLC</name>
          <address>
            <com:street1>900 Salem Street</com:street1>
            <com:city>Smithfield</com:city>
            <com:stateOrCountry>RI</com:stateOrCountry>
            <com:zipCode>02917</com:zipCode>
          </address>
        </brokerOrMarketmakerDetails>
        <noOfUnitsSold>15000</noOfUnitsSold>
        <aggregateMarketValue>3398890.21</aggregateMarketValue>
        <noOfUnitsOutstanding>215900000</noOfUnitsOutstanding>
        <approxSaleDate>12/19/2023</approxSaleDate>
        <securitiesExchangeName>NYSE</securitiesExchangeName>
      </securitiesInformation>
      <securitiesToBeSold>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <acquiredDate>08/22/2023</acquiredDate>
        <natureOfAcquisitionTransaction>Deferred Compensation</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>15000</amountOfSecuritiesAcquired>
        <paymentDate>08/22/2023</paymentDate>
        <natureOfPayment>Compensation</natureOfPayment>
      </securitiesToBeSold>
      <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
      <securitiesSoldInPast3Months>
        <sellerDetails>
          <name>Douglas K. Howell</name>
          <address>
            <com:street1>2850 Golf Road</com:street1>
            <com:city>Rolling Meadows</com:city>
            <com:stateOrCountry>IL</com:stateOrCountry>
            <com:zipCode>60008</com:zipCode>
          </address>
        </sellerDetails>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <saleDate>09/19/2023</saleDate>
        <amountOfSecuritiesSold>15000</amountOfSecuritiesSold>
        <grossProceeds>3524143.50</grossProceeds>
      </securitiesSoldInPast3Months>
      <securitiesSoldInPast3Months>
        <sellerDetails>
          <name>Douglas K. Howell</name>
          <address>
            <com:street1>2850 Golf Road</com:street1>
            <com:city>Rolling Meadows</com:city>
            <com:stateOrCountry>IL</com:stateOrCountry>
            <com:zipCode>60008</com:zipCode>
          </address>
        </sellerDetails>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <saleDate>11/20/2023</saleDate>
        <amountOfSecuritiesSold>11800</amountOfSecuritiesSold>
        <grossProceeds>2917216.79</grossProceeds>
      </securitiesSoldInPast3Months>
      <noticeSignature>
        <noticeDate>12/19/2023</noticeDate>
        <signature>/s/Wade Moss, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Douglas K Howell</signature>
      </noticeSignature>
    </formData>
  </edgarSubmission>
metadata_documents: [{"type": "144", "sequence": "1", "filename": "primary_doc.xml", "secsgml_size_bytes": 4028}]
text: 144
  0001222374
  XXXXXXXX
  LIVE
  0000354190
  Arthur J. Gallagher & Co.
  001-09761
  2850 GOLF ROAD
  ROLLING MEADOWS
  IL
  60008-4050
  630-773-3800
  HOWELL DOUGLAS K
  Officer
  Common
  Fidelity Brokerage Services LLC
  900 Salem Street
  Smithfield
  RI
  02917
  15000
  3398890.21
  215900000
  12/19/2023
  NYSE
  Common
  08/22/2023
  Deferred Compensation
  Issuer
  N
  15000
  08/22/2023
  Compensation
  N
  Douglas K. Howell
  2850 Golf Road
  Rolling Meadows
  IL
  60008
  Common
  09/19/2023
  15000
  3524143.50
  Douglas K. Howell
  2850 Golf Road
  Rolling Meadows
  IL
  60008
  Common
  11/20/2023
  11800
  2917216.79
  12/19/2023
  /s/Wade Moss, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Douglas K Howell