[1][2] He was a younger brother of the physician Sir James Robert Grant, chief medical officer at Waterloo.
He was promoted to captain in 1796 and subsequently fought under Sir Ralph Abercromby in the West Indies.
In June 1801, Grant was appointed Assistant Quarter and Barrack Master General in Tobago and held the same position in Dominica in 1802.
Serving in the latter post until 1833, Lionel Mordaunt Fraser's History of Trinidad (1971) states on the day after his departure on 22 June, the Port of Spain Gazette reported he was "hated by the negroes and detested by every independent member of the community".
[9][10] They had one daughter, Isabella Jean Margaret Grant (1842–1913), who married Lt Clinton Fraser Henshaw of the Rifle Brigade on 18 October 1859 at St James, Westminster, and had issue.