A member of the Australian Labor Party (ALP), he was a Senator for South Australia from 1962 to 1981 and held ministerial office in the Whitlam government as Minister for Works (1972–1973), Aboriginal Affairs (1973–1975), and Police and Customs (1975).

Prior to entering parliament he was an influential union leader as secretary of the Plasterers' Society of South Australia from 1945 to 1962.

[1] His father, a boilermaker by profession, was politically active and served on the Port Adelaide City Council.

[2] In 1945, Cavanagh was elected secretary of the Plasterers' Society of South Australia, a position he would hold until he entered the Senate in 1962.

[1] Cavanagh frequently appeared in the Industrial Court of South Australia and won a number of favourable award rulings for the plasterers.