Career
Blackwell was a butcher by trade. He became the assistant secretary and organiser of the state branch of the Australasian Meat Industry Employees Union in 1910, and its state general secretary in 1916. He also served as vice-president of the union"s federal council, and as its delegate to the United Trades and Labour Council of South Australia.
He served as a councillor and an alderman of the Town of Thebarton, and was mayor of Thebarton in 1918 and 1919.
He later served as state president of the Australian Railways Union for over a decade until 1931. He was elected to the House of Assembly at the 1918 election.