Phillips is the son of John Phillips of Swords. His father is a natural son of Richard Molesworth, 3rd Viscount Molesworth, whence Phillips acquires his Christian name. He first enters the Royal Navy, but on the advice of his friend Sir Joseph Banks he accepts a commission as second lieutenant in the Royal Marines on January 17, 1776. In this capacity he is selected to accompany Captain Cook on his last voyage, extending over nearly three years. He sails with Cook from Plymouth on July 12, 1776, and is with the marines who escort Cook when he lands at Hawaii on February 14, 1779.
In John Webber‘s painting “The Death of Captain Cook” Phillips is represented kneeling and firing at a native who is clubbing Cook. Phillips is himself wounded, but, after swimming back to the boat, he turns back and helps another wounded marine to the boats.
On November 1, 1780 Phillips is promoted to captain. On January 10, 1782 he marries Susanna Elizabeth, third daughter of Dr. Charles Burney (1726-1814), and sister of Frances Burney and of James Burney, Phillips’s friend, who, like him, had accompanied Cook on his last voyage. He has no further active service, but is promoted brevet major on March 1, 1794, and brevet lieutenant colonel on January 1, 1798. From 1784, for the sake of his wife’s health, he lives for a time at Boulogne, but after the French Revolution he resides chiefly at Mickleham, Surrey, not far from Juniper Hall, where Frances Burney entertains numbers of French emigres. From 1796 to 1799, during the alarm of a French invasion of Ireland, Phillips feels it his duty to reside on the Irish estates at Beleotton, which he had inherited from an uncle. On January 6, 1800 his wife dies.
After the Treaty of Amiens, Phillips visits France in 1802, and he is one of those who are seized by Napoleon on the renewal of the war. He is detained in France until the peace of 1814. During this detention he makes friends with the Prince of Talleyrand and other well-known Frenchmen. After his return to England he becomes acquainted with Robert Southey, Mary and Charles Lamb, who describe him as “the high-minded associate of Cook, the veteran colonel, with his lusty heart still sending cartels of defiance to old Time,” and with John Thomas Smith (1766-1833), whom he supplies with various anecdotes for his Nollekens and his Times.
(Pictured: Etching of Molesworth Phillips by Andrew Geddes, circa 1825, bequeathed by Frederick Leverton Harris, 1927, National Portrait Gallery, London)