In September 1759 he was appointed to the temporary command of , and, being attached to the grand fleet off Brest, was fortunate enough to fall in with the French fleet on 15 November. After watching it carefully, he despatched full intelligence to Hawke and to the Admiralty, while he himself went to warn Admiral Thomas Brodrick, then blockading Cadiz. His conduct on this occasion called forth an unusually warm encomium from the admiralty, as well as a direct intimation that 'he might very soon expect some mark of their favour' (Minute on Griffith's official letter of 17 November 1759). He was consequently confirmed to the command of the "Gibraltar", his commission as captain bearing date 11 December 1759. He continued in her until 1766, being employed in the Mediterraneanin until the peace, and afterwards on the home station. During the Spanish armament in 1770 he commanded the 90-gun for a few weeks, and in 1776 was appointed to the 64-gun , in which, early in the following year, he joined Lord Howe on the North American station, where he took part in the defence of Sandy Hook against D'Estaing in July and August 1778. He afterwards sailed with Commodore William Hotham for the West Indies, where he shared in the Battle of St. Lucia on 15 December, and in the Battle of Grenada in the following July. When John Byron resigned the command to Rear-Admiral Hyde Parker, Griffith was moved into the 74-gun ; but a few months later, on 18 December 1779, was killed in a slight encounter with the French in Fort Royal Bay, the Battle of Martinique. 'The service,’ wrote Parker, 'cannot lose a better man or a better officer.'