Career
Brennan was born and educated to elementary level in Wallsend, New South Wales and at age 14 he commenced work as a coal-miner at Wallsend Colliery. He was an office-holder in the Colliery Employees Federation from 1903 and in 1909, after leading a strike, he was convicted of conspiracy under the Master and Servant Acting and goaled at Bathurst for 3 months. Brennan resigned this appointment to contest the seat of Hamilton at a by-election caused by the death of Hugh Connell in 1934.
At the 1935 election he stood aside to allow the ALP to endorse Joshua Arthur.
He did not hold ministerial or party office.