Phillips, Molesworth (1755–1832), marine officer and adventurer, was born 15 August 1755 in Swords, Co. Dublin, son of John Phillips (d. 1779), surgeon and illegitimate son of Robert Molesworth (qv), 1st Viscount Molesworth of Swords; nothing is known of his mother. Phillips entered the Royal Navy and on 17 January 1776 accepted a commission as second lieutenant in the Royal Marines. In this capacity he was chosen to accompany Capt. James Cook on his last voyage, departing from Plymouth on the ship Resolution on 12 June 1776. During the voyage Phillips was promoted to first lieutenant (18 March 1778) and commander of the marines; he was with the escort of Cook which disembarked at Hawaii on 14 February 1779, and was one of the few eyewitnesses to Cook's fatal stabbing by natives within minutes of landing. Phillips was embroiled in the fighting before escaping to the waiting boats. The expedition continued its northern journey to the Bering sea before returning to the Thames on 4 October 1780; four days later Phillips was made captain, and after giving his account of Cook's death was lauded as a hero. In the official account published (1784) by Lt King, an officer on Resolution, Phillips emerged as the executioner of Cook's murderer, and this alone has assured him his place in history. There were contemporary voices of dissent, notably that of Capt. William Bligh, master of Resolution, who blamed Cook's death on the disorderly marines, badly commanded by the quick-tempered Phillips, but King's account was the accepted one for two hundred years till Gavin Kennedy in The death of Captain Cook (1978) disputed it.
During the voyage, Phillips had befriended Lt James Burney, son of the musician Dr Charles Burney and brother of the novelist Fanny Burney, intimates of an exclusive artistic circle including Samuel Johnson. In 1782 Phillips married Susannah (1755–1800), Dr Burney's third daughter, and was welcomed as a hero and a man of property. He inherited entailed land in Swords, and from his maternal great-grandfather, William Eccleston (d. 1720), and his uncle, William Eccleston (d. 1795), he inherited the estate of Belcotton and the townland of Termonfeckin, Co. Louth. The Phillipses lived for a time near Boulogne, but after the French revolution moved to Mickleham, Surrey, near Juniper Hall, where in early 1793 the duc de Talleyrand and other French nobles were exiled. Phillips befriended Talleyrand and assisted his passage to America when he was deported in May 1793. On 1 March 1794 Phillips was created brevet-major, and on 1 January 1798 was made lieutenant-colonel. He had retired on half-pay in 1795 in order to attend to his Irish property, and in 1796 he moved his wife and three children to his Louth estate, to the consternation of the Burneys who now deplored him as a son-in-law and wished to keep Susannah closer to home. He was persistently unfaithful, tyrannical, and profligate. A loan of £2,000 from Dr Burney was never repaid. Susannah resided four years in Belcotton, was alone there during the 1798 rebellion, took ill in December 1799, was rushed to England, and died there on 6 January 1800. Phillips did not attend her funeral, and nine months later married Ann Maturin, by whom he had at least two children; he had in addition a number of illegitimate children. He visited France with his family in 1802 and was detained under Napoleon's decree. He appealed to Talleyrand, who finally produced an order for the release of the party in summer 1804. Phillips resided the rest of his life in England, still moving in literary circles, if not those of the Burneys; Mary and Charles Lamb found him most congenial, as did the writer John Thomas Smith, to whom he supplied lusty anecdotes for Nollekens and his times. He never again lived in Ireland; by 1817, after a long series of sales, conveyances, and mortgages, he finally sold the residue of his estate for £6,000 to Thomas Fitzgerald of Louth. That year he was arrested and imprisoned in London for a debt of £27. He died at his house in Lambeth on 11 September 1832 and was buried, at his request, in the grave of James Burney in St Margaret's, Westminster.