John George Harry Hamilton was born on 6 Aug 1869, the son of George Hamilton of Skene House, Aberdeenshire. Educated at Cheltenham College and Sandhurst, Hamilton was commissioned 2nd Lieutenant with the Royal Highlanders on 8 Oct 1890 and served as Adjutant to the 2nd Battalion during the Boer War and wounded at Paadeberg and Mentioned In Despatches on 8 Feb 1901.
During WWI, Hamilton was again M.I.D.'d 22 June 1915, given the Brevet of Lt.-Col. and commanded the 154th Infantry Brigade on 17 Sep 1916.