[1] Brennan was born on 4 November 1904 at Dulwich Hill near Lewisham, Sydney, New South Wales.
[2][3] He was educated by the Sisters of St Joseph at Dulwich Hill and the Christian Brothers at Lewisham.
[1] On 21 October 1954, he was consecrated at the Holy Family Church at Parkes, New South Wales, in a ceremony led by Cardinal Gilroy.
[4] On 8 November 1953, he was enthroned at St Patrick's Cathedral in Toowoomba by Archbishop of Brisbane, James Duhig.
[3] Brennan died in office, following a long illness on 11 September 1975 at St Vincent's Hospital at Toowoomba aged 70.