He played junior hockey for the Flin Flon Bombers, Moose Jaw Canucks, and the Weyburn Red Wings from 1963 to 1966. His NHL rights belonged to the Detroit Red Wings so he turned pro with the Wings' farm team the Toledo Blades in 1966. Hornung was traded to the St. Louis Blues in 1967 but only played one game for the Blues until 1971-72 when he played 41 games. During the rest of those years he played in the minor pros. He won the Calder Cup with the Buffalo Bisons in 1970. In the NHL Hornung scored 2 goals and 9 assists in 48 games. In 371 WHA games, he scored 34 goals and 121 assists.