McCallum represented Jamaica as an amateur at the 1976 Summer Olympics in Montreal, Canada, where he was eliminated in the quarterfinals. In 1979 he won a silver medal at the Pan American Games.
As a professional he fought almost exclusively in the USA. He first became a world champion in 1984 by defeating Sean Mannion to win the WBA junior middleweight title. McCallum would defend that title six times, winning all six fights by knock out.