Admiral Robert Duff was among the youngest of the very many children of Patrick Duff of Craigston 1655 - 1731. In 1764 he married Lady Helen Duff (1739-1778) a younger daughter of his first cousin, William Duff of Braco, the scholarly first Earl of Fife ("Irish Honours"); the couple had six recorded children: Jean (b. 1765, married 1791 James Clerk of Bonnington), a son (b.1766, dsp), Robert William (b.1767, grandfather of Robert Duff), a child (b. 1775, d. young), Adam (1775-1840), and James Alexander Duff (1777-1800). His portrait was painted by Sir Joshua Reynolds for Greenwich Hospital.
On the morning of 20 November 1759, Robert Duff was lying at anchor in Quiberon Bay when his outlook gave him the intelligence of the French fleet to the southward of Belle Isle. He hastily put to sea and stood to the southward, chased by the French. Suddenly he tacked to the eastward, his men manning the rigging, cheering and throwing their hats into the sea. The English fleet had just been sighted, in hot pursuit of the French, who, partly owing to their turning aside to chase Duff’s squadron, were overtaken before they could get to a safe anchorage and were completely defeated. Two French ships struck their colours, four were sunk, and the rest were all damaged and ran for shelter. This was the decisive Battle of Quiberon Bay, ‘when Hawke came swooping down from the west’ and though Commodore Duff had no actual share in the fighting, his tactics greatly contributed to the result, and his name is always associated with the victory.
Promoted to command of The Foudroyant and served under Rodney in the West Indies,