George Hainsworth played junior hockey for the Berlin Union Jacks then moved up to senior hockey with the Berlin City Seniors and the Kitchener Greenshirts. One of the games he played for Kitchener against the Toronto Argonaut Rowing Club in the 1923 OHA playoffs was the first game that Foster Hewitt broadcast. By the end of the 1922–23 season, Hainsworth had played five seasons for the Greenshirts. At that time, Newsy Lalonde, manager of the Western Canada Hockey League (WCHL) Saskatoon Crescents, needed a goalie. On the recommendation of Montreal Canadiens’ part-owner Leo Dandurand, Lalonde signed Hainsworth to a pro contract of $2,500 per season with Saskatoon. Hainsworth played three seasons with Saskatoon before he was signed by Dandurand to play goal for Montreal in 1926. The Western league was in the process of folding, and Dandurand signed Hainsworth to a $6,500 per year contract before Toronto claimed him from the Western league players who were en masse moving to the National Hockey League (NHL). Dandurand had to pay $5,000 to Saskatoon for the rights to Hainsworth. There was a need for a top goaltender in Montreal. Georges Vezina, the Canadiens goaltender, had recently died of tuberculosis. Vezina had played every game in team history from the 1910–11 NHA season until the opening game of the 1925–26 NHL season, when the illness proved too much for him. In his memory, the team decided to create the Vezina Trophy for most valuable goaltender in the NHL.

George Hainsworth proved up to the challenge by winning the Vezina Trophy for the 1926–27, 1927–28 and 1928–29 NHL seasons. In 1928–29, he set an all-time record with 22 shutouts and a 0.92 goals against average while playing all 44 games. In 1930 he set an NHL record that still stands, going 270 minutes and 8 seconds without allowing a goal during the playoffs for the Canadiens. He backstopped the Canadiens to back to back Stanley Cups in 1930 and 1931. Hainsworth served as the Canadiens’ captain during 1932–33, becoming the second of only eight goalies to serve as an NHL team’s captain. George Hainsworth was traded to the Toronto Maple Leafs in 1933 for Lorne Chabot in a move by Dandurand to land another French-Canadian on his roster and boost attendance. Hainsworth helped the Maple Leafs reach the 1935 Stanley Cup Final. In 1936, Turk Broda won the goaltender job for Toronto, and Leaf manager Conn Smythe gave Hainsworth his outright release on November 25, 1936. Hainsworth retired, but was persuaded to join the Canadiens again after goaltender Wilf Cude was injured. Hainsworth played four more games for the Montreal Canadiens, from December 12 to 20, 1936, before retiring for good.