Born in London, the son of an Ezekiel King, he was related to the family of Edward Hyde, 1st Earl of Clarendon. From Westminster School, where he was a scholar under the care of Dr. Busby, at the age of eighteen he was elected to Christ Church, Oxford in 1681. There he is said to have dedicated himself so completely to his studies that after eight years he had read over twenty-two thousand books and manuscripts. (However, this astounding figure is reduced to about one-third by the polymath, Thomas Young, who remarks in his autobiographical sketch that King "read no fewer than seven thousand in the course of a residence of seven years at Oxford.")
In 1688, the same year in which he was made Master of Arts, he published a confutation of Varillas's account of Wycliffe; and, engaging in the study of the civil law, became Doctor in 1692, and was admitted an advocate at Doctors' Commons. He had already made some translations from the French language, and written some humorous and satirical pieces and in 1694, Molesworth published his Account of Denmark, in which he treated the Danes and their monarch with great contempt. This book offended Prince George of Denmark, the consort of Queen Anne; and the Danish Minister protested.
In 1699 he published A Journey to London, after the method of Dr. Martin Lister, who had published A Journey to Paris. And in 1700 he satirised the Royal Society — or at least, Sir Hans Sloane, their president — in two dialogues, entitled The Transactioner. In 1702, having moved to Ireland, he was made Judge of the Admiralty, Commissioner of the Prizes, Keeper of the Records in Birmingham's Tower, and Vicar-General to Dr. Marsh, the primate. King soon found a friend in Upton, one of the judges, who had a house called Mountown, near Dublin, where King frequently stayed; It was here he wrote the poem Mully of Mountown. In 1708, when Lord Wharton was sent to govern Ireland, King returned to London and published some essays, called Useful Transactions. His Voyage to the Island of Cajamai is particularly commended. He then wrote the Art of Love, a poem remarkable, notwithstanding its title, for purity of sentiment; and in 1709 imitated Horace in an Art of Cookery, which he published with some letters to Dr. Lister.
In 1710 he became a supporter of the Church, on the side of Henry Sacheverell; and was supposed to have concurred at least in the projection of the Examiner. His eyes were open to all the operations of Whiggism; and he bestowed some strictures upon Dr. Kennet's adulatory sermon at the funeral of the Duke of Devonshire. The History of the Heathen Gods, a book composed for schools, was written in 1711. The same year he published Rufinus, an historical essay; and a poem intended to dispose the nation to think as he thought of the Duke of Marlborough and his adherents.
In the autumn of 1712 his health declined and he died on Christmas Day.