When Henry enlisted at Warialda in January 1916 he stated he was a thirty seven year old Labourer and son of William O’Neill of Warialda. He had previously been rejected for service due to his bad teeth. Henry joined with the Inverell volunteers who were known as the Second Contingent of The Kurrajongs as they made their way to the Narrabri Camp and later to Armidale.
Henry became a member of the 33rd Battalion, 2nd Reinforcement which trained at Armidale and Rutherford prior to sailing from Australia on HMAT A15 Port Sydney in September 1916. After arrival in England further training was undertaken before they were sent to France in February 1917.
Henry was only four months at the Front line before he was Killed in Action on 7 June 1917 during the Battle of Messines. He was buried at Toronto Avenue Cemetery, Warneton, Belgium. His brother Sapper James O’Neill of No 1 Mining Corps died in April 1918 and was buried at Le Havre, France. No personal effects belonging to Henry were located other than his identity disc which was returned to his father.
Private Henry O’Neill’s name is recorded on the Honor Roll at the Warialda Town Hall.