MAcMillan led the University of Denver to NCAA Championships in 1958 and 1960.
MacMillan began his National Hockey League career with the Toronto Maple Leafs in 1960. He would also play with the Detroit Red Wings. Macmillan left the NHL following the 1965 season and retired from hockey altogether in 1971. He won 2 Stanley Cups with the Toronto Maple Leafs in 1962 and 1963.