Plunket, Thomas Span (1792–1866), 2nd Baron Plunket , bishop of Tuam, Killala, and Achonry, was born in Dublin, the eldest son of William Conyngham Plunket (qv), first Baron Plunket, and his wife, Catherine, only daughter of John McCausland, MP, of Strabane, Co. Donegal. He entered St John's College, Cambridge, in June 1809, graduating BA in 1814, and later received the degrees of MA (1822), BD and DD (1840) from TCD. A staunch protestant, he pursued a clerical career and held a succession of posts – curate in Kilsaran, Co. Louth (1819–26), rector and vicar of Dromore, Co. Down (1826–31), and dean of Down (1831–9) – before being consecrated bishop of Tuam, Killala, and Achonry in April 1839.
Plunket's episcopacy was defined and driven by fervent evangelicalism, partly influenced by the ultra-protestant views of his nephew William Conyngham Plunket (qv), who served as his chaplain and private secretary in the late 1850s. Plunket was an enthusiastic supporter of the Irish Church Missions and of the proselytising colony on Achill Island of Edward Nangle (qv). He published several pamphlets on missionary and doctrinal themes, such as Convert, confirmations . . . (1851), Charge delivered to the clergy of Killala and Achonry (1854), The west Galway church building fund (1860), but it was as an evangelical landlord that he gained lasting notoriety. He was censured first for absenteeism and subsequently for aggressive proselytising practices, which alienated the tenants of his estates in Co. Galway and Co. Mayo as well as local clergy. In the late 1840s he was accused of promoting evangelicalism over famine relief, and in 1854 his attempt to appropriate a building in Tuam once used by the Christian Brothers provoked rioting. Large-scale evictions from his estate in Partry, Co. Mayo (popularly attributed to the tenants’ refusal to send their children to proselytising protestant schools), caused a heated controversy that was widely covered in the press, fuelled by the catholic archbishop, John MacHale (qv), and Father Patrick Lavelle (qv). By 1860 the bishop of Orléans was raising money for catholic victims of ‘the war in Partry’, and the affair was discussed in parliament (Times, 13 Mar. 1860). Plunket claimed that the evictions were motivated by feelings of insurrection and published a letter in The Times (24 Oct. 1860) and pamphlets to that effect (Doings in Partry: a chapter of Irish history, 1860; Letter to Earl Cowley, 1861), but his actions were widely condemned.
Plunket held several public positions, including Irish privy councillor (1846), trustee for the Society for Bettering the Condition of the Poor of Ireland, ecclesiastical commissioner for Ireland (1851–66), member and vice-president of the Irish Clergy's Education Society, and president (1864–6) of the Church Education Society for Ireland, Kildare Street, Dublin. He succeeded his father as second Baron Plunket in 1854. On 26 April 1819 he married Louisa Jane, daughter of John William Foster, MP for Dunleer, with whom he had five daughters. He died 19 October 1866 at his home, Tourmakeady Lodge, Co. Galway. Collections of his papers are held in the British Library, London, and PRONI.