Born in Surrey Hills to labourer Patrick William Brennan and Kate Kealy, he attended school in Carlton and at St Joseph's CBC North Melbourne in 1915.
[1] After leaving school he moved on to the University of Melbourne where he studied law on a part-time basis.
He became a political journalist, having joined the Labor Party (ALP) around 1925 and was the editor of The Tribune, a weekly Catholic newspaper, for two years.
[2] He was admitted as a solicitor in 1935, and led classes in English and Public Speaking at the Victorian Labor College from 1941 to 1956.
[3] From 1945 to 1955 he was on the state executive of the ALP, serving as president from 1950 to 1951 and as a Victorian MLC for Monash Province from 1952, but in 1955 he was part of the split that formed the Australian Labor Party (Anti-Communist), which became the Democratic Labor Party (DLP).