Cain's NHL career started when he joined the Montreal Maroons of the NHL in the 1933–34 season. He split that season between the Maroons and the Hamilton Tigers of the OHA. In 1934–35 Cain briefly played for the Windsor Bulldogs of the IHL. With the exception of a one-game stint with the Hershey Bears in 1940–41, he would remain in the NHL for the next 11 seasons. As a member of the Maroons, Cain played on a line with Gus Marker and Bob Gracie. They were dubbed the "Green Line" and their combined offensive prowess led Montreal to their second Stanley Cup Championship in 1934–35. Cain was dealt to the Montreal Canadiens in the fall of 1938. After one season in Montreal, he was traded to the Boston Bruins for Charlie Sands and Ray Getliffe. Cain had his most productive years in Boston. Playing on a line with future Hall of Fame inductee Bill Cowley, he helped the Bruins win the Stanley Cup in 1940–41. Cain went on to win the NHL scoring title in 1943–44 with 82 points. His total set a record for points in a season which stood until Gordie Howe scored 86 in 1950–51. Despite criticism that the war-depleted league had led to a freak season - his mark was more than double his previous season high - Cain was selected as a Second Team All-Star at left wing and was runner up to Clint Smith of the Chicago Black Hawksfor the LadyByng Trophy. The following season, he scored 32 goals for Boston, but fell well short of his previous point mark, and in the season thereafter his totals plummeted further. In 1946–47 Cain was sent to the Bears of the American Hockey League and he went on to help the Bears win the first Calder Cup, the first in franchise history. Cain ended his professional career in 1949–50 as a member of the Bears. As a member of the Boston Bruins, Cain twice recorded four-goal games. Both came against the Toronto Maple Leafs, on January 11, 1940 and January 16, 1945, respectively. Cain remains the only eligible former NHL scoring champion not inducted into the Hockey Hall of Fame. He was the last active player in the NHL to have ever played for the Maroons. In total, Cain played 571 NHL regular season games. Cain's older brother Jack Cain played professional hockey in the AHL for the New Haven Eagles and the Bears. His cousin Jim "Dutch" Cain also played in the NHL.
