Colwill played junior hockey for the Lethbridge Native Sons from 1951 to 1955. He was also picked up by the Regina Pats for the 1954-55 Memorial Cup Final. He turned pro with the Saskatoon Quakers of the Western League in 1955-56. He spent his entire career in that league except for the 1958-59 season, when he played 69 games and scored 7 goals and 6 assists for the New York Rangers of the National Hockey League. Colwill retired in 1960.