Thomas was the son of William Henry and Fannie Mason of Gum Flat near Inverell. His birth was registered at Inverell in 1895. Thomas was a twenty year old Labourer when he enlisted at Inverell in January 1916. He joined other district men to form the Second Contingent of The Kurrajongs who left Inverell together on 29 February 1916 on their way to the Narrabri and Armidale camps.
He became a Private with the 33rd Battalion, 2nd Reinforcements and after training at Armidale and Rutherford he sailed from Australia on HMAT A68 Anchises in August 1916. Upon arrival in England further training was undertaken at Salisbury Plain before he was sent to France in November. During the Battle of Messines Thomas suffered a severe gunshot wound to his left hand. He was evacuated back to England where he was admitted to 1st Southern General Hospital in Birmingham. As he had lost the tops of the first and second fingers of his left hand Thomas was returned to Australia in September 1917 and the follwing month discharged medically unfit. He was granted a pension of thirty shillings per fortnight. By 1940 he was living in Queensland.
His older brother Donald served at Gallipoli and in France with the 1st Battalion 5th reinforcement. Their names are recorded on the Inverell and Gum Flat Honor Rolls.