After playing junior hockey in Saskatoon, Saskatchewan, McNab played on minor professional teams in the 1946–47 season before being called up to the Detroit Red Wings of the National Hockey League in 1947. He would play on and off with the Red Wings until 1951, playing on the team that won the Stanley Cup in 1950. He played for the Indianapolis Capitals of the American Hockey League in 1950–51. Before the 1951–52 season, he was traded by the Red Wings to the Chicago Black Hawks, but never played for the team. Back surgery kept him out of action in 1951–52 and McNab then joined the New Westminster Royals of the Western Hockey League, where he played for seven seasons, retiring in 1959. He was voted league MVP in 1955, scoring 32 goals and 81 points.