S/7678 Pte. Thomas Wishart enlisted with the 8th (Service) Battalion, Royal Highlanders (Black Watch) on 11 January 1915. It seems likely he may have had previous military training as he proceeded overseas with the battalion several months later on 10 May.
The 8th Black Watch was raised at Perth in August 1914 by Lord Sempill of Fintray, Aberdeenshire which may give some clues as to where Thomas came from, however to date there are no surviving records that hint at his origins. At the time Thomas enlisted the Highlanders were based in Aldershot and moved to Alton, Hampshire on 16 January. It seems likely that this is where Thomas joined his unit. In March they moved to Bordon where training continued, and the remainder of their equipment and supplies were received.
Thomas left Bordon on 10 May 1915 with the bulk of the battalion and embarked at Folkestone for Boulogne, where he entrained for Arques, near St. Omer. His first experience of the trenches probably occurred towards the end of May when the Highlanders briefly took over the line at Armentieres.
The summer was spent in and out of trenches around Festubert, Le Plantin and Givenchy before moving on to the Hohenzollern Sector in September. Thomas was very likely wounded at the Battle of Loos on 25 September when the battalion advanced on the Hohenzollern Redoubt. He was listed in the casualty lists early the next month and eventually discharged from service on 3 October 1916 due to his wounds.