MacNaghten, John (1722–61), murderer, was born in 1722, probably in Benvarden, Co. Antrim, elder of two sons of Bartholomew MacNaghten, landowner in Co. Antrim and merchant in Derry city, and his wife Mary (née MacManus); he also had a sister. When John was about six, his father died, leaving the family estates to his elder son, who was educated at Raphoe, Co. Donegal. He entered TCD in 1740, but left after a year. He lived as a country gentleman, was a governor of Derry workhouse in 1754, was involved in 1755 with founding one of the first farming societies in Ireland, and was high sheriff of Antrim in 1756. From his schooldays on, however, he was addicted to gambling, and eventually lost almost his whole patrimony. He was well connected, well liked, and persuasive; his friend the earl of Massereene introduced him to Mary Daniels, sister of the earl's wife and daughter of the dean of Down; they were married (14 August 1752) at St Mary's, Dublin. Despite solemn promises, MacNaghten rapidly lost still more money, and when in 1756 creditors ambushed him violently at the door of their Dublin house, the shock killed his pregnant wife. The earl of Massereene secured for him in 1757 the post of collector at Coleraine, but MacNaghten ill repaid his friend's kindness; in less than a year he embezzled £800 of public money, and his brother-in-law had (by one account) to forfeit a bond of £2,000.
In about 1760 MacNaghten spent a few weeks at Prehen, Co. Londonderry, as guest of Andrew Knox, MP for the county. Without delay, and in secret, MacNaghten courted the 15-year-old Mary Anne Knox, his host's daughter, an heiress in her own right; the girl's father refused to countenance MacNaghten's suit, and believed that the matter was closed. However, MacNaghten took advantage of the Knoxes' hospitality, and pursued Mary Ann until she agreed to read part of the marriage service before a witness; always with the proviso that her father would agree to the marriage. After further importunity on MacNaghten's part, Mary Ann told her family of the secret transaction, and they took legal action to have the contract annulled in April 1761. In November 1760 MacNaghten attempted, without success, to be selected as candidate for the parliamentary seat of Carrickfergus. His hopes of succeeding to the estates of his uncle Edmund Macnaghten, who was then 82, were crushed in 1761 when the old man, horrified by his nephew's conduct, married a young wife so that John would not inherit. Edmund Macnaghten proceeded to father two sons, and lived until he was 102 years old; he was grandfather of Sir William Hay Macnaghten (qv) and great-grandfather of Sir Edward Macnaghten (qv).
John MacNaghten is said to have fought a duel at Sligo, and to have threatened a judge who had ordered him to pay £500 damages to the Knoxes. He took refuge in Bath, but shortly, in a state of despair verging on madness, returned to pursue Mary Ann Knox. In disguise, he attempted to communicate with her while she was on a visit to Swanlinbar, the spa in Cavan; when he was again unsuccessful, he planned an ambush to carry her off. Such an abduction of an heiress was not an unknown stratagem in the period. With three accomplices, he attacked the Knox family's coach on 10 November 1761, on the road between Strabane and Derry; five bullets from MacNaghten's gun fatally wounded Mary Ann Knox. Wounded himself, he escaped and hid in an outbuilding; soldiers commanded by Sir James Caldwell (qv) arrested him, and he was tried for murder in Strabane on 11 December 1761. He ably conducted his own defence and pleaded with great pathos, but unsuccessfully, for a pardon for his servant and tenant Thomas Dunlop, who had been his accomplice. His plight and personality engaged the sympathy of the local inhabitants, and no one would make a gallows to hang him until Mary Ann Knox's uncle undertook the work himself. On 15 December, in the middle of the Lifford road out of Strabane, MacNaghten ascended the gallows; he jumped so violently from it that the rope broke. Though he could have made his escape, or appealed for a pardon, he insisted on returning to the gallows, since, as he said, he did not wish to live to be known as ‘half-hang'd MacNaghten’. Dunlop was also executed; both bodies were beheaded and buried in one grave in the local churchyard.
MacNaghten's story is still familiar in the north of Ireland, and ironically the sobriquet that he feared is that by which he is remembered. Many details and different versions of the events of his life and death are preserved in folk tradition, and there are also a number of accounts written at the time. What was left of MacNaghten's estate was inherited by his daughter, Cassandra. However, in 1767 MacNaghten's creditors received some satisfaction, and following lawsuits in 1791 and 1797 Cassandra and her husband Joseph Hardy were obliged by the court of chancery to sell Benvarden. It was bought by the merchant and banker Hugh Montgomery (1743–1832), who was known as ‘Split-fig Montgomery’.