Turnbull was born at Hamilton, Victoria to farmer Adam Beverly Turnbull and Georgina Agnes, née Drummond. He was mostly educated by his mother, although he did attend state schools for short periods. Following his father's death in 1922, Turnbull and his mother moved to Warracknabeal, where he was employed as an auctioneer. He took part in several public speaking competitions before he and his mother moved to Essendon 1933. During this time, he became interested in politics, joining the Country Party. He attempted to run for the Country Party in the House of Representatives seat of Bendigo in 1937, and attempted to take the Victorian Legislative Assembly seat of Lowan in 1940, but was unsuccessful in both.

In July 1940, Turnbull enlisted in the Australian Imperial Force and was sent to Malaya. He was captured at the 1942 fall of Singapore and was a prisoner of war for three and a half years at Changi, where he organised debates among the prisoners. At the end of the war he returned to Australia, unsuccessfully contesting the Legislative Assembly seat of Borung.

In 1946, Turnbull was elected in a by-election to the federal seat of Wimmera for the Country Party. He was subsequently discharged from the army in order to sit in the Parliament. He married tailoress Beryl Bradley on 22 December 1947 at Essendon.

Turnbull was a dedicated parliamentarian who never missed a parliamentary sitting. After his home was transferred to the newly created Mallee in 1949; he transferred there and was easily elected. He was appointed Country Party whip in 1956, and in 1968 was appointed a CBE. He was knighted in 1972 and retired from parliament later that year. He died at Bendigo on 15 January 1980, survived by his wife; they had no children.

A story told about Turnbull's interactions with Gough Whitlam (perhaps apocryphal) is that during a noisy parliamentary moment, Turnbull said "After all I am a country member". To which Whitlam retorted "I remember".^[1]

• Boadle, Donald (2002). "Turnbull, Sir Winton George (1899–1980)". Australian Dictionary of Biography. National Centre of Biography, Australian National University. ISSN 1833-7538. Retrieved 16 March 2008.