Crombie was born on October 12, 1966 in Toronto, Ontario, the son of Shirley Anne (Bowden) and David Crombie, who was the mayor of Toronto from 1972 to 1978 and a Canadian federal Cabinet Minister in the 1980s. Crombie attended Lawrence Park Collegiate Institute, where he was spotted by casting agent Diane Polley performing in a production of The Wizard of Oz