He served in the Legislative Assembly of Manitoba from 1936 to 1949 as a representative of the Social Credit League, and was a cabinet minister in the governments of John Bracken and Stuart Garson.
After the election, they surprised many in the province by providing support to Liberal-Progressive Premier John Bracken's minority government.
In 1940, Social Credit formally entered government as part of a four-party coalition, which also included the Liberal-Progressives, Conservatives and CCF.
Although Turnbull did not lead the Social Credit caucus in the house, he was selected as the party's cabinet representative and was sworn into office on November 4, 1940, as a Minister without portfolio.
Turnbull was re-elected[1] with an increased plurality, and remained in cabinet when Stuart Garson replaced John Bracken as Premier in 1943.