Pole, William Wellesley- (1763–1845), 3rd earl of Mornington , chief secretary for Ireland, was born William Wesley on 20 May 1763 at Dangan Castle, Co. Meath, second of four sons of Garret Wesley (qv), professor of music, politician, and 1st earl of Mornington, and Anne Wesley (née Hill-Trevor). Educated at Eton (1774–6), he was not a brilliant student and joined the Royal Navy in 1778; by this time he had begun spelling his surname as Wellesley, like his brothers, Richard Colley (qv), Arthur (qv), and Henry (1773–1847). A midshipman for four years, in 1781 he inherited the estates of his cousin William Pole and took the additional surname of Pole. Entering the Irish house of commons as MP for Trim, Co. Meath (1783–90), he was a committed supporter of the government. His eldest brother's friendship with the prime minister, William Pitt, gave him a useful connection at Westminster and he was found a safe seat at East Looe (1790–95). Growing frustrated at his lack of opportunities, however, he vacated the seat, and resigned himself to looking after Richard's interests while his brother was in India. The proposed legislative union roused him from his apathetic slumber and he opposed the measure vehemently. The attempt to accompany it with catholic emancipation disgusted him, and in the spring of 1801 he was furious with the behaviour of Lords Castlereagh (qv) and Cornwallis (qv). At the end of the year he returned to parliament as MP for Queen's Co. (1801–21), and supported the administration of Henry Addington. His loyalty towards government was rewarded with a minor office; in June 1802 he became clerk of the ordnance with responsibility for defending the estimates in parliament.
Out of office during the brief ministry (1806–7) of Lord Grenville (qv), he returned to office under Portland (qv) in 1807. His subsequent promotion to the admiralty made him responsible for the discussion of naval measures in parliament, and he continued to defend his brothers' reputations even when he disagreed privately with them. Although Arthur was ostensibly chief secretary for Ireland, his military responsibilities meant that he spent much of his time abroad and William began to assume some of his duties. When Arthur was awarded a peerage after the victory of Talavera he allowed William to choose his title; he decided on ‘Wellington’, much to his brother's approval. On 18 October 1809 Wellesley-Pole was appointed chief secretary for Ireland, despite the concern of the duke of Richmond (qv), who felt that his temper was too volatile. As secretary he opposed conciliation, and became a divisive influence on the catholic question. In February 1811 he issued a circular prohibiting the catholic committee from electing a convention in Ireland and followed this by blocking a meeting of the committee later in the month. There was uproar at Westminster, and the cabinet rebuked him for not having received authorisation for his actions. Nevertheless he maintained his position, and received ministerial support for a proclamation against catholics later in the year. By linking the Irish exchequer with the office of chief secretary he restored some of the authority of the Castle in Ireland, although this reform was not continued by subsequent secretaries. By 1812 he had grown tired of Ireland, and was anxious to return to England. The daily death threats did little for his spirits, although he appreciated the humour of letters signed ‘Pat Pikeman, Kit Killman, and Sam Shootman’.
With the assassination of the prime minister Spencer Perceval (11 May 1812) he was out of office, and refused to accept a position because of a newly-declared sympathy for the catholic question. Observers found this change difficult to understand, but Wellesley-Pole insisted that he had been merely following Perceval's lead in Ireland. On 22 June 1812 he spoke in favour of George Canning's pro-catholic motion, alienating himself further from the new ministry. The prestige of Wellington facilitated his reconciliation with government and in September 1814 he was appointed master of the mint. His debating skills soon led to some notable victories over the opposition, although his return to office was mocked in Dublin, where Robert Peel (qv) reported that he was ‘the theme of universal ridicule. All his choice sayings are stored up and repeated with malicious accuracy’ (Hist. parl., v, 515).
Fearing the loss of his seat in Queen's Co., he unsuccessfully applied for a barony in 1817. With the Liverpool ministry in disarray, and his own political fortunes in decline, on 17 July 1821 he was created Baron Maryborough of Maryborough, Queen's Co. By his own admission he was ‘sent to the dogs' by the government in 1823; he resigned from the mint, and never held high office again. He was master of the buckhounds (1823–30) and postmaster general (1834–5), before succeeding his older brother Richard as 3rd earl of Mornington on 26 September 1842. He died on 22 February 1845.
He married (17 May 1784) Katherine Elizabeth, daughter of Adm. John Forbes, an Irish MP, and granddaughter of the 3rd earl of Granard; they had one son and three daughters. His son, William Pole Tylney Long-Wellesley (1788–1857) succeeded as 4th earl of Mornington and 2nd Baron Maryborough .