<SEC-DOCUMENT>0001049521-25-000071.txt : 20251110
<SEC-HEADER>0001049521-25-000071.hdr.sgml : 20251110
<ACCEPTANCE-DATETIME>20251110170014
ACCESSION NUMBER:		0001049521-25-000071
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20251107
FILED AS OF DATE:		20251110
DATE AS OF CHANGE:		20251110

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Plunkett Debora A
		CENTRAL INDEX KEY:			0001699997
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-41194
		FILM NUMBER:		251467194

	MAIL ADDRESS:	
		STREET 1:		6501 LEGACY DRIVE
		CITY:			PLANO
		STATE:			TX
		ZIP:			75024

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MERCURY SYSTEMS INC
		CENTRAL INDEX KEY:			0001049521
		STANDARD INDUSTRIAL CLASSIFICATION:	ELECTRONIC COMPONENTS & ACCESSORIES [3670]
		ORGANIZATION NAME:           	04 Manufacturing
		EIN:				042741391
		STATE OF INCORPORATION:			MA
		FISCAL YEAR END:			0630

	BUSINESS ADDRESS:	
		STREET 1:		50 MINUTEMAN ROAD
		CITY:			ANDOVER
		STATE:			MA
		ZIP:			01810
		BUSINESS PHONE:		9782561300

	MAIL ADDRESS:	
		STREET 1:		50 MINUTEMAN ROAD
		CITY:			ANDOVER
		STATE:			MA
		ZIP:			01810

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	MERCURY COMPUTER SYSTEMS INC
		DATE OF NAME CHANGE:	19971112
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>form4.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-11-07</periodOfReport>

    <issuer>
        <issuerCik>0001049521</issuerCik>
        <issuerName>MERCURY SYSTEMS INC</issuerName>
        <issuerTradingSymbol>MRCY</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001699997</rptOwnerCik>
            <rptOwnerName>Plunkett Debora A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>50 MINUTEMAN ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>ANDOVER</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01810</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2025-11-07</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1700</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>73.9906</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>16833</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes></footnotes>

    <ownerSignature>
        <signatureName>/s/ Douglas Munro, attorney-in-fact</signatureName>
        <signatureDate>2025-11-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
