Art Duncan was with the Vancouver Millionaires of the Pacific Coast Hockey Association in 1915-16, but enlisted for military service in World War One the following year. He played on the 228th Battalion hockey club that began the 1916-17 season in the NHA before being sent overseas.
Duncan returned from the Great War decorated with the Military Cross. He returned to playing hockey, joining the Vancouver Millionaires in 1918-19. He remained in the Pacific Coast League for several years before looking at moving up to the NHL. He had a five-year NHL career with the Detroit Cougars and Toronto Maple Leafs in the late 1920s and early 1930s.
His pro career began in 1926 at the age of 32 with the Cougars where he served as playing coach. The Cougars would eventually evolve into the Falcons and finally the Red Wings, as we know them today. In 34 games, he scored three goals and two assists. Jack Adams replaced him as coach for the following season and Duncan decided it was time to move on.
Duncan joined the Toronto St. Pat's club which had recently been bought by Conn Smythe and renamed the Toronto Maple Leafs. In 1927-28, Duncan turned out his most successful season. He played in 44 games, scored seven goals and five assists while accumulating 97 minutes in penalties.
When Smythe purchased a young star by the name of King Clancy, Duncan retired to become the head coach of the Maple Leafs in 1930-31. Dick Irvin replaced him early in the 1931-32 season and guided the Leafs to their first Stanley Cup.