A half-length portrait facing very slightly to left, wearing captain's undress uniform (over three years) 1748-67 and a grey wig. His arms are folded and he holds the top of his sword in his left hand. Rocks are implied on the right and the sea in the distance on the left, to indicate his status as a naval officer.
Byron was a midshipman in the 'Wager', 24 guns, on Commodore Anson's circumnavigation of the world of 1740-44, during which she was wrecked on the coast of Chile. In June 1764, after this portrait was painted, he took command of the copper-sheathed frigate 'Dolphin' and the sloop 'Tamar' to locate a reported 'Pepys Island' in the south Atlantic and then attempt to find a Pacific entrance to the long-fabled North-West Passage. Arriving at the Falkland Islands, he correctly identified them with 'Pepys Island' and annexed them for Britain. After sailing through the Straits of Magellan he considered his ships 'too much disabled' to pursue his North-West Passage mission, crossed the Pacific and returned to England in May 1766. Appointed to the North American command in 1775 he remained there until 1779, when he was beaten by the French fleet under the Comte d'Estaing in an action off Grenada. Byron's service earned him the nickname of 'Foul-weather Jack' and he was the grandfather of the Romantic poet, Lord Byron.

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, of which the artist made at least one copy, may have been cut down from a larger canvas.