Grant was commissioned a second lieutenant in the Coldstream Guards on 20 February 1897, and promoted to lieutenant on 11 May 1898. He served in the Second Boer War in South Africa from 1899 to 1902, where he was part of the Kimberley relief force, and was wounded at the Battle of Belmont in November 1899. Following the end of the war he was appointed adjutant of the 1st Battalion of his regiment on 1 July 1902.