In 1867, he joined the British Army, as an ensign in the 5th Northumberland Fusiliers, later transferring to the Highland Light Infantry, in which he was lieutenant and adjutant for nearly seven years, and in 1876 was promoted captain.

[1][3] During the Second Boer War, Hildyard was posted to South Africa and commanded the 2nd Brigade from 1899 to 1900, again being mentioned in despatches and seeing active service at the Battle of Colenso.

[4] Hildyard remained in South Africa to command the 5th Division from 1900 to 1901, during which time he took part in the Battle of the Tugela Heights.

[6] French returned to the United Kingdom after the war had formally ended in June 1902, but did not relieve Hildyard of the command until 15 September 1902.

[1] In 1903, Hildyard had been appointed Colonel of the Highland Light Infantry and he continued to serve at the head of the regiment until his death in 1916, when he was succeeded by Sir William Pitcairn Campbell.