After serving his country for two years during World War I, McKinnon joined the Sudbury Wolves of the Northern Ontario Hockey Association, with whom he had played a few games over three seasons prior to his tour with the army. In 1923–24 he joined the Pittsburgh Yellow Jackets of the United States Amateur Hockey Association, and he made his NHL debut in 1924–25 with the Hamilton Tigers. In that season, he scored eight goals with three assists, mostly while playing defence. He played in 193 NHL games, scoring 19 goals and 11 assists.