William was born in Glasgow, Scotland in 1893 to James and Margaret McAllister. He attended Calderbank Public School in Glasgow and later served twelve months with the Gordon Highlanders. It is not known when he came to Australia, however he was a member of the Lithgow Pipe Band in early 1914 before moving to Inverell where he became a menber of the local Independent Pipe Band. He was employed by the Inverell Municipal Council.

William enlisted in October 1914 and became a member of the 14th Battalion, 2nd Reinforcement which departed Australia for Egypt on HMAT A46 Clan Macgillivray in February 1915. That month he was promoted to Corporal, then Sergeant. He was sent to Gallipoli where he was killed in action on 8 August 1915. William has no known grave and his name is inscribed on the Lone Pine Memorial, Gallipoli, Turkey.

His name is also among the twenty one recorded on the Calderbank War Memorial in Scotland. At Inverell William's name was recorded on the Independent Pipe Band's Honor Roll.