Hamilton, John James (1756–1818), 9th earl and 1st marquess of Abercorn , politician, was born in July 1756 in London, posthumous son of Capt. John Hamilton (1715–56) and his wife Harriet, daughter of Sir James Craggs. He was educated at Harrow (1767–71), before entering (1773) Pembroke College, Cambridge, although he never graduated. He was a contemporary of William Pitt at Cambridge, a connection that would be important later. Hamilton also entered the Middle Temple in 1773, but again seems not to have practised law. His father's death at sea (1756) meant that Hamilton was the heir presumptive to the earldom of Abercorn, held by his uncle. This expectation of future honours and wealth meant that Hamilton was able to enjoy a relatively carefree life while at Cambridge.
After a two-year European grand tour, Hamilton first entered the Westminster parliament in 1783, representing East Looe, a seat he secured through an uncle of his first wife. In parliament he quickly established himself as a vocal supporter of his old college friend, Pitt. At the 1784 election he was returned for St Germans in Cornwall, a borough controlled by his half-brother Edward Eliot, his mother's son by her first marriage to Sir Richard Eliot of Port Eliot – the Eliots, like Hamilton, were strong Pittites. Hamilton's house of commons career came to an end in 1789, when he succeeded his uncle as 9th earl of Abercorn. As well as the title, he inherited estates in Scotland, England, and Ireland. His Irish estates in Co. Tyrone and Co. Donegal comprised approximately 36,000 acres, with an annual rental of over £20,000.
In October 1790 Abercorn, with the support of Pitt, secured a promotion in the peerage, becoming 1st marquess of Abercorn. He was determined to carve out a political role for himself in Ireland, where he began to build up a strong borough interest, rekindling the family interest in Strabane, while also purchasing the borough of Augher, also in Co. Tyrone. He also developed close links with the Knox brothers, Thomas (qv) and George (qv), sons of the 1st Viscount Northland (qv), who became the leaders of the Abercorn interest in the Irish parliament. Abercorn's serious approach to politics could be seen not just in his cultivation of a borough interest, but also in the preparation of a parliamentary list – the only Irish eighteenth-century parliamentary list not produced by the government – by Thomas Knox for his use in 1791, which detailed the various Irish political interests. Abercorn, through the influence of George Knox, became an advocate for catholic emancipation, leading in 1792 to an unusual proposal from John Keogh (qv) and Theobald Wolfe Tone (qv), playing on Abercorn's known vanity, that he should seek the Irish viceroyalty and install a pro-catholic administration. This proposal came to nothing, although Abercorn did meet the Catholic Committee's delegation in London in 1793.
Abercorn himself was determined to secure the lord lieutenancy from the time of his arrival on the Irish political scene in 1789–90. His intentions are clear from his correspondence in the years 1790–93, which includes several explicit and implicit references to a possible viceroyalty in succession to the incumbent earl of Westmorland (qv), another Cambridge contemporary of Pitt. The Catholic Committee's scheme – brought to Abercorn through George Knox, an old friend of Tone – was conjured up precisely because of Abercorn's known desire to succeed the anti-catholic Westmorland. Abercorn's machinations were not successful, partly because he had a greater opinion of Pitt than the prime minister had of him. Pitt complained of Abercorn's ‘intolerable pride’ and thought he would be ‘troublesome in Ireland, and resolved never to send him there’ (Elliot, Tone, 187). Abercorn's only Irish appointment would be his nomination to the privy council (1794), while the disaster of the Fitzwilliam (qv) viceroyalty in 1795, an administration operated on Abercorn principles, suggested that any Abercorn government would have suffered the same fate.
Abercorn's political star never fully recovered, and he spent much of the 1790s preoccupied by local matters, mostly involving his Co. Tyrone militia regiment, in which he was involved in a struggle with his erstwhile ally, Thomas Knox. Abercorn eventually resigned his colonelcy in 1798 during the Abercromby (qv) affair, in protest against the commander-in-chief's comments about the state of the Irish army. He was a strong supporter of the act of union, though much of his correspondence at this time was preoccupied with securing the £15,000 compensation for both of his boroughs at Augher and Strabane. After the union Abercorn supported the Addington ministry, before supporting Pitt during the latter's last ministry. Abercorn's reconciliation with Pitt, following their slightly frosty post-1793 relationship, was completed in 1805 when he became a knight of the garter, an honour Pitt had denied him in 1794. Much of Abercorn's post-union career was, however, spent in semi-obscurity, accentuated by his domestic woes, which saw him lose all but one of his children before his own death in 1818. His career is difficult to assess; he enjoyed many of the natural advantages of an aristocratic leader, including connections on both sides of the Irish Sea, excellent powers of oratory, a large fortune, and a significant electoral connexion. He had, as Malcomson has argued, ‘most of the qualities and opportunities to break the mould of Anglo-Irish politics in the last decade of the eighteenth century’ (Malcomson, ‘Marquess of Abercorn’, 65). His failure to do so was partly based on the disparity between his ambitions and the reality of politics, as well as his dependence on Pitt, who, although personally friendly, was suspicious (perhaps rightly) of Abercorn's political temperament.
Outside politics, Abercorn was an active patron of architecture, getting the esteemed English architect Sir John Soane to carry out extensive works on his Co. Tyrone seat Baronscourt, as well as to build his English seat, the Priory in Middlesex, where Abercorn spent much of his time, and where he died on 27 January 1818.
He married first (1779) Catherine Copley (d. 1791), with whom he had four sons and two daughters, although only one son, James (d. 1814), reached adulthood. His second marriage, to his cousin Lady Cecil Hamilton, ended in divorce (1799), when Hamilton discovered that his wife was committing adultery with his first wife's brother, Capt. John Copley. He married thirdly (3 April 1800) Lady Anne Hatton (b. 1764), daughter of Arthur Saunders Gore, 2nd earl of Arran. His only surviving daughter married Lord Aberdeen, the future prime minister. Hamilton's grandson, James, who did not attain his majority until 1832, succeeded him as 10th earl, and achieved one of his grandfather's great desires half a century later, when he gained (1868) the title of 1st duke of Abercorn, which his grandfather first sought in 1790. Abercorn's extensive correspondence is in the PRONI (D.623).