Knox, John (1758–1800), soldier and MP, was born 9 October 1758, second among seven sons of Thomas Knox (qv), 1st Viscount Northland, and his wife Anne née Vesey (d. 1803), second daughter of John, 1st Lord Knapton, and Elizabeth, eldest daughter of William Brownlow (qv) of Lurgan. He was commissioned captain in the 67th Regiment of Foot (5 February 1778) and major in the 36th Foot (23 November 1780). As MP for Killybegs, Co. Donegal (1777–83), and Dungannon, Co. Tyrone (1790–94), he was attached to the Abercorn interest in parliament and usually supported the government, voting against legislative independence (1780) and for catholic relief (1778, 1793). He resigned his seat in 1794, probably to take up military duties. In the 1780s and early 1790s he fought in the Mysore wars in India against Tipu Sultan. As lieutenant-colonel of the 52nd Regiment he served under Cornwallis (qv) and commanded three regiments of the central division in the attack on Seringapatam (6 February 1792), which finally defeated Tipu. Afterwards he was promoted to major-general and colonel of the 9th Foot.
In December 1796 he was appointed one of three Ulster district generals under the overall command of Gen. Gerard Lake (qv). Based in Dungannon, Knox commanded the mid Ulster district, which was seen as crucially important in preventing the spread of the ideas of the United Irishmen from Antrim and Down into west Ulster. Possessing considerable military skill, political shrewdness, and extensive local knowledge, he was consulted regularly by Thomas Pelham (qv), the chief secretary. With the growth in number of the United Irishmen in the spring of 1797 Knox advocated extreme measures to pacify Ulster, including the declaration of martial law and the disarmament of the province through terror. Closely involved in developing the plans of his brother Thomas (qv) to raise a yeomanry force, he devised a test oath obliging yeomen to swear that they were not United Irishmen, and encouraged them to wear orange emblems. Though he disapproved of the Orange Order, he believed that the danger of insurrection justified recruiting Orangemen into the yeomanry, concluding that they were the only men in the north who could be depended on to support the government. He often used Orange yeomen to search for arms, partly because of their local knowledge but mostly because they were sure to antagonise the United Irishmen, and he believed that ‘upon that animosity depends the safety of the central counties of the north’ (Blackstock, 239).
As early as April 1797 he was advocating union, arguing that it was the only way to prevent separation since there would always be discord between Britain and Ireland so long as they had separate legislatures. He recommended that once the country had been subdued by severe military coercion, it should be offered parliamentary reform, catholic emancipation, and an administration purged of sinecures, on condition that it acceded to a union. A strong critic of the venality and selfishness of the Irish aristocracy, he favoured legislation compelling landlords to offer preferential terms on leases to sitting tenants.
In January 1798, as rebellion drew closer, he developed a comprehensive plan for the defence of Ulster against French invasion. To make scattered yeomanry corps into a more effective force, in April 1798 he formed them into county brigades on permanent duty, and set up supplementary yeomanry corps to take over local policing functions in the event of a rising or invasion. He also assisted Dublin Castle in implementing the yeomanry brigade system throughout the rest of the country. These measures contributed to preventing a major United Irish rising west of the Bann. During the rebellion Knox dispersed rebel gatherings at Maghera (7 June) and Toome (9 June), but mid Ulster remained largely undisturbed.
Cornwallis regarded him as one of his most intelligent and capable generals, and after the rebellion Knox was ordered to the West Indies. He had already embarked at Portsmouth, but with the French invasion on 22 August 1798 he was recalled to Ireland and landed at Galway in early September with a large detachment of troops. Similarly, when Cornwallis believed that a French expedition to Ireland from Brest was due to sail in May 1799, he recalled Knox from England, where he was on the point of sailing for St Helena, and immediately dispatched him to Ulster to supervise the province's defence. When the expected invasion did not occur, he served in the duke of York's expedition to Holland, concluding the armistice at Alkmaar between the British and French armies and signing his name to the subsequent treaty (18 October 1799). He was later involved in peace negotiations in France in spring 1800, and was afterwards appointed governor general and commander-in-chief of Jamaica, but drowned on his passage to Jamaica on the Babet in October or November 1800; he never married. His family clung to the hope that he had survived, and nominated him for the family parliamentary borough of Dungannon. His death contributed to a family superstition that a Knox would be drowned in every generation.