After the war, Watson joined the Toronto Dentals in a playoff series against the Hamilton Tigers, which the Tigers won. For the 1919–20 season, he joined the new Toronto Granites, the OHA team from the Toronto Granite Club. Led by Watson, the Granites won the Allan Cup in 1921–22 and 1922–23, with Watson named a first-team all-star in both seasons. They then represented Canada at the 1924 Winter Olympics, winning the ice hockey gold medal. At the Olympics, Watson scored 36 goals in five games as the Canadian team outscored the opposition 132-3 over six games. In one game against Switzerland, Watson scored 13 goals.