<SEC-DOCUMENT>0000354190-25-000047.txt : 20251125
<SEC-HEADER>0000354190-25-000047.hdr.sgml : 20251125
<ACCEPTANCE-DATETIME>20251125170944
ACCESSION NUMBER:		0000354190-25-000047
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20251121
FILED AS OF DATE:		20251125
DATE AS OF CHANGE:		20251125

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Mead Christopher E
		CENTRAL INDEX KEY:			0001737644
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-09761
		FILM NUMBER:		251522513

	MAIL ADDRESS:	
		STREET 1:		2850 GOLF ROAD
		CITY:			ROLLING MEADOWS
		STATE:			IL
		ZIP:			60008

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Arthur J. Gallagher & Co.
		CENTRAL INDEX KEY:			0000354190
		STANDARD INDUSTRIAL CLASSIFICATION:	INSURANCE AGENTS BROKERS & SERVICES [6411]
		ORGANIZATION NAME:           	02 Finance
		EIN:				362151613
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		2850 GOLF ROAD
		CITY:			ROLLING MEADOWS
		STATE:			IL
		ZIP:			60008-4050
		BUSINESS PHONE:		630-773-3800

	MAIL ADDRESS:	
		STREET 1:		2850 GOLF ROAD
		CITY:			ROLLING MEADOWS
		STATE:			IL
		ZIP:			60008-4050

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	ARTHUR J. GALLAGHER & CO.
		DATE OF NAME CHANGE:	20190819

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	GALLAGHER ARTHUR J & CO
		DATE OF NAME CHANGE:	19920703
</SEC-HEADER>
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<TYPE>4
<SEQUENCE>1
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<DESCRIPTION>PRIMARY DOCUMENT
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    <periodOfReport>2025-11-21</periodOfReport>

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        <issuerName>Arthur J. Gallagher &amp; Co.</issuerName>
        <issuerTradingSymbol>AJG</issuerTradingSymbol>
    </issuer>

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            <rptOwnerName>Mead Christopher E</rptOwnerName>
        </reportingOwnerId>
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            <rptOwnerStreet1>2850 GOLF ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>ROLLING MEADOWS</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60008-4002</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
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            <isOfficer>1</isOfficer>
            <officerTitle>VICE PRESIDENT</officerTitle>
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    <aff10b5One>0</aff10b5One>

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                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionTimeliness></transactionTimeliness>
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    <footnotes>
        <footnote id="F1">Each share of phantom stock represents a right to receive one share of Gallagher common stock.</footnote>
        <footnote id="F2">These shares represent awards under the Age 62 Plan, a nonqualified deferred compensation plan of the Company, which have been deemed invested in Company common stock at the election of the reporting person.  Participants vest in these awards when they attain age 62, or after a one-year period for participants who have attained age 61.</footnote>
        <footnote id="F3">Granted on May 1, 2017.</footnote>
        <footnote id="F4">One-third of this stock option becomes exerciseable on each of the 3rd, 4th, and 5th anniversaries of the grant date.</footnote>
        <footnote id="F5">Granted on March 15, 2018.</footnote>
        <footnote id="F6">One-third of this stock option becomes exerciseable on each of the 3rd, 4th, and 5th anniversaries of the grant date.</footnote>
        <footnote id="F7">One-third of this stock option becomes exercisable on each of the 3rd, 4th, and 5th anniversaries of the grant date.</footnote>
        <footnote id="F8">Closing price of Gallagher common stock on February 28, 2025.</footnote>
        <footnote id="F9">Each notional stock unit represents a right to receive one share of Gallagher common stock.</footnote>
        <footnote id="F10">The notional stock units become payable following the reporting person's separation from service with Gallagher.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Seth Diehl, by power of attorney</signatureName>
        <signatureDate>2025-11-25</signatureDate>
    </ownerSignature>
</ownershipDocument>
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</SEC-DOCUMENT>
