A half-length portrait to the left showing Onslow in his vice-admiral's undress uniform of the 1795-1812 pattern, wearing the ribbon and star of the Bath and the Camperdown medal.
Richard Onslow rose rapidly in the Navy thanks to his uncle, Arthur Onslow, who was speaker of the House of Commons. He was in Vice-Admiral George Pocock’s fleet in the East Indies as lieutenant in the ‘Sunderland’, the ‘Grafton’ and the ‘Yarmouth’, 1758–60. On 11 February he was made commander of the ‘Martin’ and was promoted captain of the ‘Humber’ on 14 April 1762. The ship was wrecked off Flamborough Head that September but Onslow was acquitted; the pilot was deemed culpable.
From January 1766 until 1769 he commanded the frigate ‘Aquilon’ in the Mediterranean and then, from 12 October 1770, the ‘Diana’ in the West Indies. He was given the ‘Achilles’ on 18 January 1773 and returned to Britain. He was then appointed to the 64-gun ‘St Albans’ on 31 October 1776 and employed off North America with Howe and in the West Indies with Hotham, including the capture of St Lucia. In February 1780 in the 74-gun ‘Bellona’ he joined Admiral Geary’s Channel Fleet. He was on half pay from June 1783. In 1789 he was appointed to the ‘Magnificent’ at Portsmouth, but was unemployed from September 1791 to 1796. In the meantime, he was promoted rear-admiral of the white on 1 February 1793 and vice-admiral on 4 July 1794. Onslow was port admiral at Portsmouth in 1796 and that November was made second in command of Admiral Duncan’s North Sea Fleet in the ‘Nassau’, his ship involved in the mutinies at Yarmouth in 1797. On 25 July 1797, he moved to the 74-gun ‘Monarch’ and played a leading role in the Battle of Camperdown on 11 October that year. Onslow was made a baronet and the Corporation of London presented him with a 100-guinea sword and the freedom of the City. He retired from service and sea, becoming admiral of the red on 9 November 1805.