In 1737, Elliot was commissioned as major of the 2nd Troop of Horse Grenadier Guards, of which he was made lieutenant-colonel in 1741. He fought at both Dettingen and Fontenoy, but resigned his commission in 1746. His eldest sister's son, George Augustus Eliott (later Lord Heathfield, defender of Gibraltar), was one of his subordinate officers in the 2nd Troop of Horse Grenadier Guards.