Jardine saw service in several theatres of the Seven Years' War, including the Raid on Rochefort, the Invasion of Martinique (1759) and the Invasion of Guadeloupe (1759), and in 1762 was in Gibraltar for its defence. His subsequent career was as second lieutenant on 11 September 1762, first lieutenant on 28 May 1766, and captain-lieutenant on 28 April 1773.