The 31-year old defender becomes the third former Sky Blues player to join the Heart, following fellow championship winners Clint Bolton and John Aloisi.
Colosimo has signed a multi-year deal with the Heart after a proposed deal with Korean club FC Seoul fell over due to visa issues.
Heart coach John van ‘t Schip said Colosimo’s addition to the squad will be a very handy one for the new club, especially if he is successful in his bid to make the Australian World Cup squad.
“Simon has wonderful technical ability and will provide fantastic composure in defence,” the Dutchman said.
“Making the World Cup squad would not only be a highlight of his career, but also allow the club to have a presence on the international stage.”