Thornton attempted to be drafted in the 1996 NHL draft but was not selected by any team. He was then drafted into the NHL by the Toronto Maple Leafs in 1997, 190th overall, Thornton never played for Toronto and was traded to the Chicago Blackhawks during the 2001–02 season. After six seasons back and forth between the NHL and AHL between the Chicago and Anaheim Ducks franchises, Thornton won his first career Stanley Cup in his final season with the Ducks in 2006–07.