1747-94. Baptised on 26 June 1747, he was the eldest surviving son and successor of James Sinclair of Durran and of his wife Elizabeth Dunbar, the daughter of Sir Patrick Dunbar of Northfield. He was a descendant of King James V of Scotland, and was the uncle of Admiral Robert Honyman.
Sinclair was commissioned lieutenant on 29 January 1771 and promoted commander of the armed ship Queen 20 on 3 September 1781. Following service in the North Sea the Queen entered Sheerness in January 1783 for repairs after being rammed by another vessel, and here Sinclair transferred briefly to the sloop Termagant 22. On 16 January he was posted captain and he joined the Hyaena 24, going out to the west coast of Africa in June and returning with despatches in October. During December he sat on the court martial investigating the conduct of Captain Evelyn Sutton of the Isis 50 at the Battle of Porto Praya on 16 April 1781, and from January 1784 the Hyaena served on the Irish station from where she returned at the expiration of her commission in March 1785.
During the Spanish Armament Sinclair commissioned the frigate Iphigenia 32 in May 1790, and he sailed to join the Grand Fleet in Torbay from Portsmouth in July. Continuing in service, he arrived at Portsmouth in May 1791 with pressed men for the Russian Armament, and after paying the Iphigenia off in September he then recommissioned her in the same month to go out on a cruise, seeing further service off Wales and Ireland.
On 10 February 1793, whilst still commanding the Iphigenia, he briefly flew the flag of Rear-Admiral John MacBride as the commander-in-chief in the Downs, whilst also engaging in convoy duty. On 16 February off Cherbourg he captured the privateer Elizabeth, the second privateer to be taken in the French Revolutionary War, and Midshipman Richard Curry was charged with taking the prize into Portsmouth.
In March 1793 the Iphigenia departed for the Leeward Islands with Rear-Admiral Alan Gardner’s squadron, and she served thereafter on the Jamaican station, participating in the successful campaign to occupy parts of San Domingo from 19-21 September. She later joined the Penelope 32, Captain Bartholomew Samuel Rowley, in the capture of the French frigate Inconstante 40 off San Domingo on 25 November, although her consort did the bulk of the fighting and the Iphigenia did not suffer any casualties. In the same year Sinclair succeeded to his father’s estates, at which point he became known formally as Patrick Sinclair of Durran. On 16 March 1794 his frigate took the French vessels Actif 16 and Espiègle 12, both being bought into the Navy.
Captain Sinclair died at St. Domingo on 5 May 1794 during the operations that saw the capture of the capital, Port-au-Prince, on 4 June.
He married Anne Sutherland, the daughter of Robert Sutherland of Langwell, and had issue two sons and a daughter. His first son, Patrick, died at Gosport in 1791, his second son, James, died as the lieutenant of marines aboard the Beaulieu 40, Captain Stephen Poyntz, on 22 July 1801 during the cutting out of the French sloop Chevrette from Camaret Bay, and his daughter married Captain John Worth of the Navy.