The sitter entered the navy as a young boy and served as a king's letter boy between 1683 and 1686. In 1687 he became a lieutenant and two years later he commanded the fireship Charles and for the next few years he remained actively employed in the channel, on the coast of Ireland, in the Bay of Biscay and on the coast of Portugal. In 1696, the year the present portrait was made, he served on the Rupert in the West Indies. Following the deaths of his superior officers, Dilkes took command of the ship and brought the squadron home the following year. In 1699 he was seriously injured when his ship was wrecked on the coast of Ireland. In 1703 he was promoted to rear-admiral of the white and experienced success in subsequent naval campaigns. In 1704 he sailed with Sir Cloudesley Shovell to join Rooke at Lisbon and took an active part in the battle of Malaga as rear-admiral of the White squadron. In recognition of his services, he was knighted by Queen Anne in 1704. He died from a fever and 1707 and was survived by his wife Mary, daughter of Murrough O'Brien, 1st Earl of Inchiquin and a son, Michael O'Brien Dilkes who became an army officer.
A portrait of the sitter in civilian dress and with a naval battle scene in the background by Sir Godfrey Kneller is in the National Maritime Museum (inv. no. BHC2659).