Joseph Forbes Duncan (3 June 1879 – 1 December 1964) was a Scottish trade unionist and politician. Born in in Banffshire, Duncan grew up in near Aberdeen and was educated at Robert Gordon's College. He left school aged fifteen then, when he was seventeen, moved to London to work for the Post Office. However, he suffered from poor health, and moved back to Scotland in 1898, finding work in Aberdeen. While there, he became politically active, joining the local Clarion Club, and lecturing on Marxism.