Douglas was born on October 20 1904, in Falkirk, Scotland. In 1910, his family emigrated to Canada, where they located in Winnipeg. During WWI, the family returned to Glasgow but came back to Winnipeg in 1920.
On June 15 1944 Douglas led the Saskatchewan CCF to power in the provincial general election, winning 47 of 53 seats.
When the CCF became the New Democratic Party in 1961, Douglas became its first leader, serving until 1971. After his resignation, he kept his seat in the House of Common until 1979.
Douglas died of cancer on February 24 1986 at the age of 81.
He was also the father of Canadian actress Shirley Douglas, and the grandfather of Kiefer Sutherland.