Oval miniature in watercolour on ivory, with the right edge cracked, in an oval gold suspension locket. At some time the frame has had a horizontal hinged brooch pin added across the back, though the pin itself is now missing. The back is glazed (with a nearly horizontal crack) and the gilt letters 'JH' in the centre, and contains a roughly coiled lock of dark brown hair, presumably the sitter's. Hillyar is shown head and shoulders, turned slightly to his left but looking out slightly to left of the viewer. He has grey (probably powdered) and slightly curly hair cut short in the 'Regency' style and wears captain's uniform of 1795-1812 pattern with the two epaulettes denoting over-three-years seniority. The left lapel of the coat is buttoned over, with a black stock and the wings of a white shirt collar just visible above it. The colours have faded and there are some spots of detachment, but his eyes were probably originally blue or blue-grey. The ivory may also have shrunk slightly, possibly with water damage round the edge, since it does not exactly fit the frame.

Hillyar was the son of a naval surgeon. He entered the Navy in 1779 and after service in the American War and the ensuing peace, won a commission from Lord Hood on 8 March 1794 for his services at Toulon and in Corsica early in the French Revolutionary War. As a lieutenant he served under Sir Robert Stopford in a number of ships, initially the 'Aquilon' including at the Battle of 1 June 1794, and on promotion to Commander on 16 April 1800 commanded the 'Niger', armed 'en flute' as a troopship to the Mediterranean, where he was involved in boat actions and similar operations. Nelson had a very high regard for him, and was also aware that he was the main support of his mother, sisters and a brother, and was instrumental in securing his advance to post-captain on 29 Februrary 1804. The armament of the 'Niger' was increased to justify this and he remained in her in the Mediterranean until 1807. He was subsequently flag-captain to both Sir Eliab Harvey and Rear-Admiral Pickmore in the Baltic, and Saumarez then put him in command of the 36-gun frigate 'Phoebe' there. In her he later sailed to the East where he was present at the taking of Mauritius in 1810 and Java in 1811. In 1813, still in 'Phoebe', he went to attack American fur interests in the Pacific North-West but sent on a consort to do this and diverted to hunt for the larger 46-gun American frigate 'Essex', which was raiding British shipping off South America. Eventually he found and blockaded her in Valparaiso. On breaking out the Amercan lost a topmast in a squall, which sufficiently disabled her to make her anchor, where Hillyar pressed home the advantage and captured her - though accused of taking an unfair advantage. In 1830–31 he commanded the 'Revenge', 74 guns, under Sir Edward Codrington, and for a short time as senior officer in the North Sea during the siege of Antwerp. He was then in the 120-gun 'Caledonia' on the coast of Portugal during 1832 and early 1833. He became KCH in January 1834, a rear-admiral on 10 January 1837 and KCB on 4 July 1840. Hillyar married Mary, a daughter of Nathaniel Taylor, naval storekeeper at Malta, in 1805, and had three daughters and three sons. The latter included Admiral Sir Charles Farrell Hillyar (d. 1888) and Admiral Henry Shank Hillyar. He died at Torpoint, Cornwall, on 10 July 1843, and was buried in the parish churchyard at Anthony.

The crack in the ivory and probably other damage to this item appear, from NMM neg. 8744, to predate its arrival in the Museum, which may have been as early as 1932 as a loan, though only purchased for it by Sir James Caird from Miss Phoebe Rees, a descendant of Hillyar, in October 1934.