Background
Borthwick was born in Murrayville in north-western Victoria, and attended state schools in Cowangie and Walpeup before gaining a scholarship to study at Ballarat Grammar School between 1936 and 1939.
Borthwick was born in Murrayville in north-western Victoria, and attended state schools in Cowangie and Walpeup before gaining a scholarship to study at Ballarat Grammar School between 1936 and 1939.
Borthwick was a Liberal Party member of the Victorian Legislative Assembly for the electorates of Scoresby (1960–1967) and Monbulk (1967–1982). From 1940 to 1957, he was a bank officer for the State Bank of Victoria, then worked as an insurance representative. In December 1942, Borthwick enlisted in the Royal Australian Air Force.
Borthwick was elected to the Victorian Legislative Assembly in a September 1960 by-election for the seat of Scoresby triggered by the death of the sitting Member of Parliament, Sir George Knox.
At the 1967 state election, Borthwick switched to the new seat of Monbulk.