A half-length portrait to right wearing flag officer's undress uniform, 1748-67, with the coat buttoned across. He wears his own hair.

Keppel was the second son of the Earl of Albemarle, and one of a powerful Whig family who came to England in 1688 with William III. In 1740 he joined Commodore Anson on his four-year voyage round the world in the 'Centurion'. In 1749 he went as commodore to the Mediterranean, and took Joshua Reynolds with him (again in 'Centurion'). This voyage marked the beginning of a close lifelong friendship between them. Reynolds was en route for Italy, where he stayed for two years. 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 after early work in his native Devon travelled to Italy in 1749. In 1753 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. This portrait was painted for Lord Rockingham, leader of the Whig faction to which Keppel belonged, and was given by him to Lady Rockingham. Reynolds probably kept the painting in his studio for several years, during which time he may have worked on it, as well as making copies. He later wrote to the sitter to say that he had an engraving made from it, of which the National Maritime Museum also holds impressions and the original copper plate. Reynolds is thought to have painted portraits of Keppel fifteen times.