Grant was promoted to captain in 1907 and to major in 1916. During World War I he served in the Persian Gulf in 1915–16, France and Belgium in 1917 and Mesopotamia in 1918. After the war he served in Afghanistan in 1919, and then as lieutenant colonel in command of the 13th Rajputs in the Waziristan campaign (1919–1920). He was awarded the Distinguished Service Order "for distinguished service rendered in the Field with the Waziristan Force, 1920–1921." He was Assistant Adjutant General at the headquarters of the Army of India 1925–28, and Deputy Director of the Auxiliary and Territorial Force in India 1928–29. He retired in 1929 with the rank of colonel and was appointed a Companion of the Order of the Bath in the King's Birthday Honours of that year. He was ceremonial Colonel of the 10th Gurkha Rifles 1934–47.