During the 2016 World Indoor Bowls Championship pairs they were beaten finalists, losing out to fellow Scots Stewart Anderson and Darren Burnett.

[2] Duncan won a bronze medal in the fours at the 2016 World Outdoor Bowls Championship in Christchurch with Alex Marshall, Paul Foster and Iain McLean.

[3] In 2018 he was selected as part of the Scottish team for the 2018 Commonwealth Games on the Gold Coast in Queensland[4] where he claimed two gold medals in the Triples with Darren Burnett and Derek Oliver[5] and the Fours with Marshall, Oliver and Foster.

[6][7] Once again partnering Colin Walker the pair reached the semi-finals during the 2019 World Indoor Bowls Championship.

[10] In 2024, Duncan won his first Scottish National Bowls Championships, by winning the fours with Bonnyrigg BC.