Forbes spent his junior career with the Kingston Canadians and St. Catharines Fincups of the OMJHL, and won a silver medal with Canada at the 1977 World Junior Championships. Following his draft, Forbes split the 1977–78 season between Boston and their AHL-affiliate, the Rochester Americans. Forbes played in Rochester for the 1978–79 season, and was claimed by the Edmonton Oilers in the 1979 NHL Expansion Draft.