Percy (Smithson), Hugh (1715–86), duke of Northumberland , lord lieutenant of Ireland, was born Hugh Smithson 19 December 1715 at Newby Wiske, Yorkshire, the only son of Langdale Smithson, landowner, and Philadelphia Smithson (née Revely). Raised as a catholic, he converted to the Church of England after the death of his father, and succeeded his grandfather as 3rd baronet in 1733. Educated at Christ Church, Oxford, he became MP for Middlesex (1740–50). He married (16 July 1740) Elizabeth Seymour, daughter of Baron Percy and granddaughter of the 6th duke of Somerset, who disapproved of the match; they had two sons and one daughter. After the death of his father-in-law (7 February 1750), who had been created earl of Northumberland five months earlier, he succeeded to the title and by an act of parliament took the name and arms of Percy. On 29 March 1757 he was made a knight of the garter.
On 27 April 1763 he was appointed lord lieutenant of Ireland, and he arrived in Dublin to be sworn-in on 22 September. To celebrate the news, the English poet Christopher Smart wrote an ‘Ode to the right honourable the earl of Northumberland’ which he published the following year. It contained explicit criticisms of the ‘lurking priests’ in Ireland and concluded with an elegant tribute to Northumberland: ‘In pity to our sister isle/ With sighs we lend thee for a while . . . We never had a man to spare/ Our love cou'd less afford’ (Williamson, 360). Considered the most handsome man of his day, and greatly assisted by the pomp of his viceregal court, Northumberland was a popular figure in Dublin.
Taking control of the parliamentary management in Ireland, he was disturbed by the behaviour of some of the leading politicians, especially the speaker, John Ponsonby (qv), and was determined to quell any independent conduct. As the year progressed he considered punishing individuals to reassert the authority of the administration, but was persuaded to pursue a cautious line by Lord Halifax (qv), the secretary of state, who had himself served as lord lieutenant. After the close of the parliamentary session he decided to return to England on 9 April 1764, where he was involved in intrigues to remove the prime minister, George Grenville; he was replaced by three lords justices, Archbishop George Stone (qv), the earl of Shannon (qv), and John Ponsonby. The attempts to change the ministry failed, and Grenville insisted on Northumberland's removal as lord lieutenant, which occurred in February 1765.
In recognition of his service to the crown, on 22 October 1766 he was created Earl Percy and duke of Northumberland, and on 28 January 1784 Lord Lovaine, baron of Alnwick. He died 6 June 1786 at Sion House, Middlesex, and was buried at Westminster Abbey. His eldest son, Hugh Percy (formerly Smithson), succeeded as 2nd duke of Northumberland, and his grandson, Hugh Percy (qv), 3rd duke of Northumberland, was lord lieutenant of Ireland 1829–30.