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. 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.

Reynolds was the most influential figure of the century in British painting. He borrowed poses from the old masters and created portraits in a style that was deemed fresh and modern, and yet dignified the status of the sitter.