Thomas was born in Manchester, probably in the Ardwick area where he was educated at the local Higher Grade school. The family later moved to 406 Wellington Road, Heaton Chapel, where he lived with his parents, Joseph and Mary. He trained to be an engineer and, in his spare time, was a member of the Cheshire Yeomanry. He emigrated to Australia in about 1913, when he was 19, and worked as a stationhand and horseman. He enlisted into the army on 4 January 1915 at Alderley, Brisbane. He was then aged 21 years and 9 months.
Thomas' service file is available on-line at the Australian National Archives and this shows him to have been just under 5' 10" tall and he weighed 10 stone 2 pounds. He was of fair complexion with blue eyes and dark brown hair. Thomas had recorded his religious denomination as Church of England.
Whilst in training, Private Thomas Seddon, 733, was assigned to the machine gun section of the 25th Battalion, Australian Imperial Force. By March he had been promoted to acting Sergeant. At the beginning of the month, he went absent from camp without leave for a brief period and was formally admonished. The following month, he again went absent and was fined. He embarked to go on active service from Brisbane on board HMAT Aeneas on 29 June.
Thomas disembarked in Egypt and he remained there until 4 September when he embarked at Alexandria to go into action at Gallipoli. He had lost his sergeant's stripes and was a private again, but was promoted back to Lance Corporal on 20 September. Only six days later, he was admitted to 7th Field Ambulance suffering with dysentery. It was very common complaint in the unsanitary conditions at Gallipoli. He returned to duty on 3 October. In December, he was promoted to Corporal but again fell ill. This time, he was admitted to No. 1 Canadian Stationery Hospital suffering with pyrexia. His service file is unclear when he returned to duty but he appears to have ill again and, on 3 January 1916, he was at a field hospital on the Greek island of Mudros, where he remained until 11 January. He was then evacuated, aboard the hospital ship Asturias, to Alexandria in Egypt where he was admitted to 21st General Hospital. A few days later he was moved to 1st Auxiliary Hospital at Heliopolis and, on 9 February, he was invalided home to Australia aboard the Nestor.
On 5 June 1916, he again left Australia to return to active service. He had been promoted to Corporal, with 8 as his new service number, and assigned as an original and early member of the 11th Machine Gun Company. The troopship, A30, arrived at Alexandria on 12 July
The Companies had been formed in February 1916 by merging the four battalion machine gun sections in each brigade into one unit. They were equipped with 16 Vickers heavy machine guns. These were heavy pieces and each gun had several men in its crew to carry it and the ammunition. It was a devastating weapon, used to cut down attacking infantry. It was also used to support an attack by maintaining a heavy fire against a specific target, keeping the enemy's heads down.
In November, Thomas fell ill again with enteric fever and was evacuated from France to Southampton. On 15 February 1917, Thomas was commissioned as a Second Lieutenant.
It has not been possible to locate a copy of the Company's War Diary in the UK and the unit is not mentioned in the Australian Official History of the War as being in action in the days prior to Thomas' death. As such, it is not possible to establish exactly what happened to him. His service record shows that he was shot on 17 March. He was admitted to 9th Australian Field Ambulance, which treated him for the wounds in his chest and back. The bullet had penetrated his lung. The next day, he was evacuated to 2nd Australian Casualty Clearing Station (a field hospital, staffed by military surgeons). He died there ten days later and was buried in the adjacent Cemetery by the Rev. B C Wilson.
The role of Casualty Clearing Station was to undertake emergency surgery and to stabilise the casualty so he could be moved to permanent "stationery" hospitals on the Channel coast or in Britain. It is most unusual for a man to stay for more than a couple of days at a CCS - he was either well enough to be moved or he was dead. The fact that Thomas remained there for ten days means that, either he remained too ill to be moved, or the surgeons determined that there was absolutely no hope for him. In any event, he will have been made as comfortable as possible in the circumstances.