Parnell (- Hayes), William (1777–1821), writer, landlord, and MP, was born probably in August 1777 (some sources suggest 1780), third son of Sir John Parnell (qv) and his wife Letitia Charlotte, daughter of Sir Arthur Brooke of Colebrook, Co. Fermanagh. His elder brother was Sir Henry Brooke Parnell (qv), later Lord Congleton. After attending Eton, he entered Trinity College, Cambridge (1794). On the death of his father (1801) he inherited the Avondale estate in Co. Wicklow and changed his name to Parnell-Hayes (Sir John Parnell had been left the estate by his cousin, Samuel Hayes). He expressed an early interest in literature, forming friendships with Mary Tighe (qv), who dedicated a sonnet to him, and Thomas Moore (qv), whose famous lyric ‘The meeting of the waters’ was written on a visit at Avondale. A didactic novel entitled Julietta, or, the triumph of mental acquirements over personal defects (1802) has been ascribed to Parnell, but he is remembered mainly for his political writings on Ireland.
His political outlook was influenced by the writings of Thomas Jefferson and Edmund Burke (qv), as well as his own experience as a landlord at Avondale (despite widespread and intense rural unrest, he maintained good relations with his tenants). In his 1804 pamphlet, An inquiry into the causes of popular discontents in Ireland by an Irish country gentleman (2nd ed. 1805), he attributed Irish unrest to the Elizabethan conquest and confiscation of land, the tithe question, and the sectarian structure of the state. He also comprehensively denounced the act of union, and advocated catholic emancipation, themes that were expanded in the 1807 pamphlet An historical apology for the Irish catholics (three editions by 1808), favourably reviewed by the Rev. Sidney Smith in the Edinburgh Review (1807). The pamphlets embody Parnell's liberal political outlook and his emphasis on parliamentary liberalism, as well as his distinctive rhetorical style; all of which were a crucial influence on his grandson, Charles Stewart Parnell (qv).
Parnell's later publications include Sermons, partly translated, partly imitated, from Massillon and Bourdaloue (1816), intended to be used for religious instruction in catholic schools; and a politically driven historical novel, Maurice and Berghetta; or, The priest of Rahery: a tale (1819), which was caustically reviewed in the London Quarterly Review. Parnell defended his novel in another pamphlet, A letter to the editor of the Quarterly Review (1820). In August 1817 Parnell was elected as MP for Co. Wicklow, retaining the seat in the general elections of 1818 and 1820, while also serving as deputy lieutenant for the county. In 1820 he published A letter on the potato diet of the Irish to the editor of the Quarterly Review, which expressed unease at the widespread reliance on a single food crop. He died 2 January 1821, at Castle Howard, Co. Wicklow.
Parnell married (1810) Frances (d. 1813), eldest daughter of the Hon. Hugh Howard of Castle Howard, Co. Wicklow; they had one son, John Henry, and a daughter, Catherine, who married the writer and lexicographer George Vicesimus Wigram. Correspondence with Denis Scully (qv) is in the NLI; and with Earl Fitzwilliam (qv), in the Sheffield archives.