Born in Kilmarnock, Scotland, Colin Mochrie and his family moved to Canada when he was just 8 years old. He attended Langara College's Studio 58, a theater conservatory in Vancouver, and worked several improv shows at Expo 86, an event marking Vancouver's 100th anniversary. He later moved to Toronto and was hired by the show's touring manager - and his future wife Debra - to star in Second City's comedy troupe. He remained with Second City for three years before becoming the director of the touring company.
Mochrie first auditioned for Whose Line Is It Anyway? during the show's second season, but did not receive the part. Never one to be easily discouraged, he auditioned again two years later and landed a position on the show.