He signed a three-year contract with the Maple Leafs on October 8, 2002, after winning a position on the team's defence out of training camp.

He was paired with Bryan McCabe and picked up his first NHL point assisting on the only Maple Leafs goal in the game.

[11] At the onset of the 2005–06 season, Colaiacovo did not play well enough to warrant a place on the team and was sent to the new AHL affiliate, the Toronto Marlies.

[12] On November 8, 2005, Colaiacovo was recalled due to an injury to Aki Berg[13] and he scored his first career NHL goal against the Washington Capitals.

[14] On January 23, 2006, Colaiacovo missed a hip check on Václav Varaďa in a game against the Ottawa Senators, smashing head-first into the boards.

[16] Colaiacovo recovered fully from his concussion, but later injured his hand in his first game back into the Marlies lineup.

[21] On November 24, 2008, Colaiacovo was traded by the Maple Leafs, along with Alexander Steen, to the St. Louis Blues in exchange for forward Lee Stempniak.

"[30] With the lockout-shortened 2012–13 season, again largely affected by injury, Colaiacovo was bought out on a compliance from the final year of his contract with the Red Wings on July 3, 2013.

[33] The Blues added Colaiacovo after learning that defenceman Jordan Leopold would be out eight weeks due to hand surgery.

[36] He was signed to a one-year, two-way contract for $625,000, brought in to replace the injured Braydon Coburn and Andrew MacDonald.

[41] On November 26, 2016, he belatedly signed as a free agent with Adler Mannheim of the German Deutsche Eishockey Liga for the remainder of the 2016–17 season.

[46] Colaiacovo's twin brother Paulo is a former professional hockey player, and his cousin, Matt Finn (born February 24, 1994), was selected by the Toronto Maple Leafs in the second round, 35th overall, of the 2012 NHL Entry Draft.