A three-quarter-length portrait slightly to left facing to right in captain's (over three years) undress uniform, 1748-67. This uniform was introduced in 1748 immediately before the portrait was painted. His right hand is thrust into his waistcoat and he wears a hat and his own hair. In the left background is a rock face with foliage and on the right the ships of his squadron are shown together with the 'Centurion', 54 guns, flying his commodore's broad pendant.

Keppel, the second son of the Earl of Albemarle, was one of a powerful Whig family of Dutch origin, who came to England with William III. In 1740 he served under Commodore Anson in the 'Centurion' on his four-year voyage round the world. This portrait was probably painted at Port Mahon, Minorca, during August and December 1749 when Reynolds had accompanied Keppel to the Mediterranean on a mission to negotiate against the depredations of Barbary corsairs. Lord Edgcumbe had introduced Reynolds to Keppel in early 1749 and on 11 May the painter sailed with him (again in the 'Centurion') from Plymouth for Minorca. He spent the rest of the year there, painting portraits of the British garrison. In January 1750 he set off independently for Italy, where he stayed for two years to travel and study. This was the first of many portraits of Keppel painted by Reynolds and marked the beginning of a close lifelong friendship between them. In 1758 Keppel commanded a small expedition, which captured the island fortress of Goree, off Dakar on the West African coast. At the Battle of Quiberon Bay, 20 November 1759, he commanded the 'Torbay', 74 guns, and played a notable part by sinking the French 'Thesée', 74 guns. In 1761 he commanded the naval forces at the capture of Belle Ile and in the following year was second-in-command to Sir George Pocock at the capture of Havana. During this time he became a rear-admiral. On this expedition his elder brother, Lord Albemarle, was Commander-in-Chief and another brother was a general officer on his staff. Keppel commanded the Channel fleet in the early years of the American War of Independence, 1775-83, but found the fleet unprepared. On 27 July 1778 in the 'Victory', 100 guns, he led the fleet in an indecisive battle with the French off Ushant. His second-in-command, Sir Hugh Palliser, gave him inadequate support and the resulting quarrel split the Navy. Keppel, a Whig, was tried by court-martial, at which Palliser, a Tory, conducted the prosecution. When Keppel was acquitted he became the hero of the hour but the whole affair was politically charged. Keppel retired from active service, entered Parliament as MP for Surrey, and became a Viscount in 1782.

In 1740 Reynolds was apprenticed to the portrait painter Thomas Hudson (1701-90) and began portrait work in his native Devon. In 1753, on his return from Italy, he set up in London and rapidly began to make a name as portrait painter, profoundly influenced by his time in Italy. He became the first President of the Royal Academy in 1768 and was knighted in 1769. He was the most influential figure of the century in elevating British painting and portraiture. Reynolds borrowed poses from the old masters and by 1759 he had created social portraits in a new style that were deemed fresh and modern, and yet dignified the status of the sitter. The portrait is inscribed 'The Honourable Commodore Augustus Keppel', and signed and dated 'Josh Reynolds 1749'.