Cowie, 32, was released by Wigan on Friday and held talks with Aberdeen, but the ten-times capped former Watford and Cardiff player has opted for the Tynecastle club.
He arrived at Riccarton this morning to complete paperwork after agreeing terms. He will go straight into the squad for Sunday’s Scottish Cup tie with Hibs.
Head coach Robbie Neilson spoke of his delight at adding experience to the squad.
“I’m delighted to get Don signed up,” Neilson told the club’s website. “He’ll bring experience to the table, which is invaluable when you’re trying to blood younger players into the first team.
“He’s played in the Scottish top flight before so knows our game, and he’s played at the highest level down south and won a Championship, so I know he’s a winner.
“Having played in England, he’ll show the players here the level they’ll have to get to if they have aspirations to play there themselves.
“He’s a great capture and I’m certain he’ll prove to be great value for this club.”
Meanwhile, Hearts have had a second bid for Dundee United player John Souttar turned down. The Jambos face stiff competition from clubs in England to sign the 19-year-old, who is out of contract this summer.
They want a quick deal now rather than sign Souttar on a pre-contract agreement and let a tribunal set the amount of compensation United would be due. The latest bid is around £120,000, however Tannadice officials are not keen to sell at that price.