The Rangers defender, who can operate at both full-back and centre-back, will move along the M8 to join Eva Olid’s side after her contract expires on July 1.
By signing the one-year deal, with the option of an additional year, Brownlie becomes the club’s first ever new recruit to put pen to paper on a full-time contract.
Hearts announced their status as a semi-professional side in March and will go forward with a hybrid of full-time and part-time players.
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Brownlie, who formerly played for Hibs, Celtic and Everton, has impressed across the last three seasons for Rangers, who won the SWPL 1 title this past campaign, ending Glasgow City’s 14-year dominance of the top division.
Hearts boss Olid is looking to add experience to the club over the summer after going with a squad mostly made up of teenagers last term. Brownlie, at 28, fits the bill.