Walter Leslie Duncan (14 February 1883 - 28 May 1947) was an Australian politician. Born in Armidale, New South Wales, he was educated at state schools before becoming a clerk, and was President of the Labor Council of New South Wales in 1911. A member of the Labor Party, he joined the Nationalists in the wake of the 1916 split over conscription. Duncan enlisted in the military in 1917, leaving in 1919 to successfully contest the Senate for the Nationalists. A strong supporter of Billy Hughes, he was excluded from the party along with Hughes in 1929 and joined the Australian Party, before being reaccepted into the United Australia Party in 1931. He resigned from the Senate in 1931. He was also a Director of the Adelaide Steamship Company for many years. Duncan died in 1947.