Thomas was born at Lauriston, VIC (near Kyneton) in 1892 to Timothy O'Leary and Mary Ann Woods. Thomas had a brother, James, who is also remembered in the Avenue.
Thomas was a labourer and gave his address as Bacchus Marsh, VIC when he enlisted in the AIF, 7th Battalion on the 24th of August 1914 aged 21 years and seven months - only a few weeks after was was declared. He embarked aboard the HMAT A20 Hororata in October and disembarked in Egypt in early December.
During the landing at Gallipoli on the 25th of April 1915 Thomas suffered a gunshot wound to the chest and died(1)(2) later that day. He was buried at sea.