Thomas was born to George and Annie Arkinstall at Inverell where his birth was registered in 1887. At the age of twenty eight he enlisted at Paddington NSW stating that he was a single man, a plumber by trade and had served a five year apprenticeship with Mr. D. Scott at Inverell.
He joined the 1st Field Company Engineers, Reinforcement 1 and sailed for Egypt from Melbourne on HMAT A35 Berrima just before Christmas 1914. At the beginning of 1916 he was promoted to Corporal. Three months later his unit was sent to France. In June he was mentioned in despatches ‘for distinguished and gallant service’ whilst with the Mediterranean Expeditionary Force.
In 1917 Thomas was awarded the Military Medal for ‘valuable work in exploring a large and unknown portion of newly evacuated enemy territory for the location of communication trenches and other new works … Altogether he spent 20 continuous hours out in the newly occupied territory, under heavy fire, without food or rest of any kind.’ (Commonwealth Gazette No 133, 21 August 1917)
Thomas eventually received a Commission and became a Lieutenant with the 4th Battalion. He returned home in February 1919.