Plunket, John (c.1668–1738), Jacobite conspirator, was by his own account ‘born at Dublin and bred up when a boy at the Jesuits’ College at Vienna, that is, a Roman Catholic, but not in any orders’ (Howell, State trials, xvi, 194). He held a doctorate in civil law from Vienna, but his early career is very obscure. Certain references in the state papers in the 1690s may concern him: a John Plunkett was ordered to be arrested on suspicion of high treason in 1690, a Jacobite plotter named ‘Mr Plunket’ was mentioned in 1695, and a John Pluncket had a licence to stay in England in 1698.
Plunket approached Britain's tory ministry in March 1712 with discoveries of whig plots to put the Elector George of Hanover on the English throne by means of an invasion and coup d'état. There was deep discontent among English whigs, and England's Dutch and Austrian allies, over the conduct of the peace negotiations at Utrecht and the ministry's willingness to make a separate peace with France; the alleged conspiracy appears to have had some basis in the correspondence of certain whigs. The leading ministers, the earl of Oxford and Henry St John, regarded Plunket more sceptically than some of their colleagues, and, unlike some tories, did not judge that publication of the allegations would be profitable. Nonetheless, Oxford made use of the alleged plot to alarm Queen Anne, and influence her in favour of a peace and against the duke of Marlborough (qv) and Prince Eugene of Savoy, then visiting England.
Oxford took Plunket into the service of the government, encouraging him to believe that it was committed to the restoration of Queen Anne's half-brother, the old pretender James III. Plunket went to the Netherlands to gain more information on the plot, but while he was there he insinuated himself into the confidence of the French plenipotentiaries, as well Dutch, Hanoverian, and English whig notables, in pursuit of his own designs to bring about a Jacobite restoration. He undertook, for the same purpose, a mission to Paris and the Jacobite court at Bar-le-Duc in the autumn of 1713.
In 1721 Plunket plotted with an English Jacobite barrister named Christopher Layer, setting out with him in April 1721 for Rome. Layer, believing Plunket's knowledge of several languages would be useful, paid his expenses and they stopped on the way at Paris, where they discussed their plot with the Irish general in the French brigade, Arthur Dillon (qv). On arriving in Rome in May 1721 they were received by James III. After their return to England, Plunket's correspondence with Dillon about his recruitment of British soldiers and other preparations for an invasion and uprising in England were intercepted by the government. Layer was arrested in September 1722, and Plunket in January 1723. The Layer plot was subsidiary to that of Francis Atterbury, bishop of Rochester, whose chaplain and fellow plotter was another Irishman, the Rev. George Kelly (qv).
Though Layer was tried for treason and executed, lack of firm evidence prompted the government to proceed against Plunket, as well as Kelly and Atterbury, by the unusual method of bills of pains and penalties. Plunket was first interrogated by a committee of the house of commons, which reported that ‘though he endeavoured by his dress, appearance, and behaviour, to represent himself to the committee as very inconsiderable, and no ways equal to the part he was taxed with, yet a great number of letters from persons of the first quality abroad, were found among his papers, in which he is treated with great intimacy and confidence’ (Howell, State trials, xvi, 194–5).
Subjected by act of parliament to forfeiture of property and imprisonment at the king's pleasure, Plunket and Kelly were incarcerated in the Tower of London. Kelly, younger by twenty years, escaped in 1736 but Plunket remained till, suffering from the stone, he was removed from the Tower on 21 August 1738 to be operated on by the renowned surgeon William Cheselden. On 24 August 1738, the day after the operation, he died aged seventy. His burial expenses, and the surgeon's fee (£126), were paid from public funds, while his books, money and clothes (‘of small value’) were collected by a nephew, Thomas Plunket, his only recorded relative. (The Sergeant Matthew Plunket, a soldier who gave evidence that he had been suborned by John Plunket, was a protestant Irishman, and apparently not related.)
Plunket's career certainly displayed elements of fantasy and delusions of grandeur, but he moved with remarkable ease among important Jacobites and the statesmen and diplomats of the great powers of Europe. He also had contacts among a wide range of Irish expatriates, such as John Hackett, the merchant and Jacobite agent of Rotterdam (almost certainly a son of Sir Thomas Hackett (qv)), and Daniel Arthur (qv) and Sir Richard Cantillon (qv), Irish bankers in France, as well as Englishmen with Irish connections such as Sir William Ellis (qv) and William Penn (qv).
Some of Plunket's papers, seized in 1722, are preserved among the Walpole papers in the British Library (Add. MS 74001).