Duncan began his career with Brothers (Rockhampton) in 1945. Duncan played 3 seasons with Brothers. In 1948, Duncan moved to Brisbane and joined Valleys. Duncan played 11 games over 2 seasons with Valleys (4 tries). In 1950 Duncan joined Home Hil. In 1951, Duncan joined Newtown (Toowoomba). Duncan played 3 seasons for Newtown. In 1954 Duncan moved back to Brisbane, joining the Western Brisbane Panthers. Duncan was a West Brisbane’s 1954 premiership and 1956 Grand Final side member. Duncan played 54 games for Wests Brisbane over 3 seasons (20 tries).
Duncan played 6 games for Toowoomba from 1951-52 (2 tires). Duncan played 17 games for Brisbane from 1948-57 (5 tries). Duncan played 24 matches for Queensland from 1948-55 (8 tries). Duncan played 22 test matches for Australia from 1948-55.
In 2006, Duncan was inducted into the Australian Hall of Fame. Since 2007, the Man of the Match in the Intrust Super Cup Grand Final has been awarded the Duncan Hall Medal. In 2008 Duncan was selected as a prop in the Australian and Queensland Teams of the Century, as well as in the second -row in the Toowoomba and South West Teams of the Century. In 2008, Duncan was selected as one of Australia’s 100 Greatest Players. In 2009, Duncan was inducted into the Queensland Sports Hall of Fame. In 2018, Duncan was inducted into the NRL Hall of Fame. In 2022, Duncan was selected as a prop in the BRL Team of the Century.
Duncan passed away on January 18 2011.