Jackson, William (1737?–95), protestant clergyman, journalist, and revolutionary, was born probably in Ireland, the youngest of the four sons of an official in the prerogative court in Dublin, and his wife (née Gore), both of whom were Irish. The eldest son, Richard, was vicar general to Michael Cox (qv), protestant archbishop of Cashel. Ordained in England in the established church, William Jackson acquired a reputation in London both as a preacher at Tavistock Chapel, Drury Lane, and as a journalist writing for, or editing, the Public Ledger, Morning Post, and Whitehall Evening Post. For a while he was in a debtors’ prison. He went to Ireland as chaplain and private secretary to the 2nd earl of Bristol when the earl held the office of lord lieutenant (October 1766 to August 1767). The earl, however, did not visit Ireland; Jackson's expectations of further promotion were dashed and so he returned to England.
In 1775 Jackson took up the cause of Elizabeth Chudleigh (b. 1720), known as the duchess of Kingston, a woman of immodest dress and uncouth language who, having separated from her husband, the earl of Bristol's younger brother, Augustus John Hervey, appeared openly as concubine of the 2nd duke of Kingston (1760), married him (8 March 1769) shortly after being divorced a mensa et thoro (11 February), and on his death inherited his fortune (1773). The duchess quarrelled with the playwright Samuel Foote over a comedy called ‘Trip to Calais’ (not performed), in which she was shown up as ‘Lady Kitty Crocodile’. Jackson himself, now famous as her chaplain, secretary, and protagonist, was characterised by Foote in a revised version, entitled ‘The Capuchin’ (performed in the summer of 1776), as ‘Dr Viper’. Jackson's riposte, in a newspaper he edited, was to vilify Foote, for which Foote took an action against the newspaper, thereby bringing about Jackson's dismissal and his financial dependence on the duchess. Only Foote's death brought an end to the quarrel. The duchess, however, was found guilty of bigamy in April 1776; she moved to Paris, followed by Jackson, who lived near her until her death (26 August 1788). A pamphlet, The life and memoirs of Elizabeth Chudleigh, afterwards Mrs Hervey and countess of Bristol, commonly called duchess of Kingston (1789), was ‘very probably’ by Jackson (Madden), he perhaps being disappointed at being unnoticed in the duchess's will and desirous of ingratiating himself with the earl-bishop of Derry, Frederick Augustus Hervey (qv), another brother of her late husband.
Soon after the revolution Jackson was residing in Paris and keeping company with democrats; he appears to have been giving English lessons (1791) and he attended the banquet given by English-speaking residents of Paris at White's Hotel, passage des Petits-Pères, on 18 November 1792. In February 1794, at the height of the terror, he returned, aged fifty-eight, to London on a secret mission to a French official, Nicholas Madgett (qv) (d. 1813), his object being to ascertain the degree of support in Great Britain and Ireland for a French invasion. On 1 April he arrived in Dublin and dined with Leonard MacNally (qv), whom he had known in London in the 1780s. MacNally introduced him to the United Irishmen Simon Butler (qv) and Edward Joseph Lewines (qv); Lewines took him to Newgate prison to meet Archibald Hamilton Rowan (qv), whom Jackson had probably known in Paris, a mutual acquaintance there being Rowan's brother-in-law Benjamin Beresford. Rowan introduced him to James Reynolds (qv) (d.1808) and Theobald Wolfe Tone (qv); all spoke freely, Tone drawing up a memorandum on the state of Ireland, which he gave to Jackson. A companion and supposed friend, John Cockayne, having alerted the authorities, Jackson was arrested on a charge of high treason and his papers were seized (28 April); Rowan and Reynolds fled Ireland and Tone was permitted to leave after settling his affairs. At his trial at Dublin high court a year later (23 April 1795) Jackson was defended by John Philpot Curran (qv) assisted by MacNally. The evidence given in court by Cockayne was damning, and Jackson was found guilty. But just before being brought up for judgment (30 April), he took poison. He fell senseless in the dock and died after a few minutes, thereby evading the law by which his property would have been forfeit had sentence been pronounced. His large public funeral, organised by Rowan's law agent, Edward Crookshank Keane (the radical attorney to whom Lewines was apprenticed), ended with his interment at St Michan's burial ground, Church Street, Dublin.
Jackson married twice. His second wife (who benefited financially from his suicide), son, and daughter were living on the continent in 1820. William Jackson wrote at least two pamphlets besides that on Elizabeth Chudleigh: An answer to the declaration of the king of England respecting his motives for carrying on the present war (1793), considered by R. R. Madden (qv) to be ‘a very democratic production . . . and Gallican in its politics’, and Observations in answer to Mr Thomas Paine's Age of reason (1795), a defence of Christianity. Some of his sermons were published after his death as Sermons on practical and important subjects (1795). Jackson's portrait appeared in Walker's Hibernian Magazine for May 1795.