He was the third son of the Church of Ireland minister John Beresford, 4th Marquess of Waterford and his wife, the former Christiana Leslie.

[1] On 3 July 1879 at Ulundi, Zululand, South Africa, during the retirement of a reconnoitring party, Captain Lord William Beresford went to the assistance of Sergeant Fitzmaurice of the 24th Regiment, whose horse had fallen and rolled on him.

The Zulus were coming in great numbers, but Lord William, with help from Sergeant Edmund O'Toole of the Frontier Light Horse.,[7] managed to mount the injured man behind him.

He was, however, so dizzy that Sergeant O'Toole, who had been keeping back the advancing Zulus, gave up his carbine and, riding alongside, helped to hold him on until they reached safety.

Together, Lily and William were the parents of one child: He died at Deepdene, Dorking, Surrey on 30 December 1900 from peritonitis at the age of 53.