He played junior hockey for the Toronto Young Rangers from 1935 to 1938 and signed as a free agent by the Montreal Canadiens in 1938. Thomson played mostly for the New Haven Eagles but did play in 7 games for Montreal in 1939-40. In 1940 he was traded to the New York Americans but never played for that team. He played for their farm team the Springfield Indians, When the Americans folded in 1942 Thomson was picked up by the Toronto Maple Leafs. He split the 1942-43 season between the Leafs and the Providence Reds. After that season Thomson played senior hockey until he retired in 1946.