1739-1814. He was born in Dundee Scotland on 24 January 1739, the son of Alexander Duncan who was the town clerk, and of his wife, Isabel Crawford.
Having seen early employment in the merchant service he entered the navy in May 1755 as an able seaman aboard the Nassau 70, Captain George Cockburne, and was rated midshipman in the following year. He continued in that vessel under the command of Captain James Sayer, seeing service in the Mediterranean in 1756 and in the following year in North American waters. After a year from February 1758 aboard the Newark 80, Captain William Holburne, he briefly joined the America 60, Captain Hon John Byron, going out to the Mediterranean where he was immediately moved to the flagship of Vice-Admiral Thomas Broderick, the Prince 90, Captain Joseph Peyton, serving as a midshipman for four months. Equally he was only briefly aboard the Namur 90, Captain Matthew Buckle, flagship of Admiral Hon Edward Boscawen before that vessel returned home.
He was commissioned lieutenant of the ancient guardship Barfleur 80 on 21 September 1759, moving at the end of the following year to the Hampton Court 64, Captain Carr Scrope. With this vessel he enjoyed a more active period, serving at the reduction of Belleisle in 1761 and at the capture of Havana in 1762 where the ship was commanded by Captain Alexander Innes. In October 1762 he joined the Temeraire 74, Captain Richard Bickerton, remaining at Jamaica before going on half-pay at the peace of the following year.
Duncan was promoted commander on 26 May 1768, and from 1769-72 commanded the brig Wasp in home waters 8 before once more going on half-pay.
On 7 February 1776 he was posted captain of the newly commissioned Eagle 64, going out to North America three months later with the flag of Vice-Admiral Lord Howe, the new commander-in-chief. He was aboard this vessel during the New York campaign of July-October 1776, and when the Eagle survived an attack by the submersible Turtle on 6 September. Captain Duncan then led the Naval force in operations against the Connecticut town of Danbury in April 1777 having assumed the duties of captain of the fleet whilst Roger Curtis became captain of the Eagle. He was present in the Philadelphia campaign of August-November 1777 where he superintended the flat-boat landings in the Elk River, and at the defence of New York in July 1778 and operations off Rhode Island in August 1778. Shortly afterwards the Eagle returned to England upon Lord Howe resigning his command of the North American station.
In September 1780 Duncan joined the Medea 28, going out to North America in October where he took the Morning Star 18 on 14 January 1781 and fought at the Battle of?Cape Henry on 16 March 1781. Further captures were the Protector 26 on 5 May, on this occasion being in company with the Roebuck 44, Captain Andrew Snape Douglas, the privateer Phoenix on 1 June, and the Rover 20 off Salem on 20 June. His command was on hand at the capture of the Belisarius on 4 August, took the Marianne 12 on 13 August, the Favourite 14 on 29 August, and was present at the Battle of the Chesapeake on 5 September 1781 before returning home during the following month.
From November 1781 until April 1782 Duncan had the Ambuscade 32, and from 19 April to 5 December 1782 he commanded the Victory 100, flagship of Admiral Lord Richard Howe in the Channel, being present in the summer campaign of April-August 1782 and at the relief of Gibraltar on 18 October.
In?August 1783 he arrived in Nova Scotia to become commissioner for Halifax dockyard having been appointed to that office by his friend Howe, now the first lord of the Admiralty. He came home in 1799 to seek medical treatment, assumed a similar position at Sheerness in 1800, and on 1 January 1801 became deputy comptroller of the Navy, a position he relinquished on 7 June 1806 when he retired to Dartmouth
He died in Dartmouth on 7 October 1814.
Duncan married Mary French at St. Saviour?s Church, Dartmouth, on 27 November 1761. A son, Henry Duncan, entered the Navy in 1781 but was lost off the coast of Newfoundland in the Scout 18 in November 1802. Additionally he had a daughter, Isabella and son, Arthur French.
His connection to Lord Howe was enhanced by his being a resident of Dartmouth where Howe was the local MP.