Archdale (Archdall), Mervyn (1763–1839), army officer and MP, was born 27 April 1763, eldest son among four sons and eight daughters of Col. Mervyn Archdall (1725–1813) of Castle Archdall, Co. Fermanagh, and Trillick, Co. Tyrone, and his wife the Hon. Mary (eldest daughter of William Henry Dawson (1712–79), 1st Viscount Carlow, and sister of the 1st earl of Portarlington). The antiquary Mervyn Archdall (qv) (1723–91) was a relative. Col. Mervyn Archdall, founder of the modern Castle Archdale, was a Volunteer colonel and a pioneer member of the Irish Whig Club; though he supported relaxation of the penal laws, he opposed catholic emancipation and had little regard for the rhetoric of Henry Grattan (qv). He refused the offer of a peerage to support the parliamentary union, and – though elected to parliament for Fermanagh in 1801 – did not attend Westminster.
In 1782 his son Mervyn Archdale was commissioned into the 12th Dragoons; he served in the Mediterranean from 1792, lost an arm in Egypt (1801), and was then transferred to the staff in Ireland. In 1802 he succeeded his father as MP for Fermanagh, retaining the seat till May 1834. Sir Robert Peel (qv) considered him ‘a very independent supporter of government’ (quoted in Jupp). Believing that he had not had due professional reward, Archdale voted consistently against catholic relief, and against the reform bill in 1832. In May 1805 he was awarded a papal gold medal and the rank of major-general; in 1813 he became governor of Fermanagh, in 1815 lieutenant-governor of the Isle of Wight, and in 1819 a trustee of the Irish linen board. He was also grand master of the Orange Order in 1818–22, between the end of Peel's chief-secretaryship and the first year of Richard Wellesley (qv) as lord lieutenant. The order in this period was on the defensive: the central leadership needed strengthening against unauthorised Orange bodies (a move that itself evoked further internal dissent); and the Irish government, with new resources of law enforcement at its disposal, depended less on the ‘loyal’ population, and was readier to confront any demonstration from the Orange side. After sitting in ten parliaments for Fermanagh, Archdale resigned the seat in 1834 and was succeeded by his nephew Mervyn Edward Archdale (qv). Members of the family continued to represent Fermanagh and its successor constituencies for a further century, ending with Sir Edward Mervyn Archdale (qv) in 1938.
He married (7 November 1805) Jane (d. 7 January 1851), daughter of Gustavus Hume Rochfort (1750–1824), MP for Co. Westmeath (1798–1800, 1801–24); they had no children, and after Archdale's death (26 July 1839) the estate passed to his brother William.