Lawlor, Hugh Jackson (1860–1938), church historian and dean of St Patrick's, Dublin, was born 11 December 1860 at Ballymena, Co. Antrim, third son of John Hilliard Lawlor (b. 1819), bank manager, and his wife Catherine, daughter of Lieut-col. John Elliott Cairnes (1785–1847). John Lawlor was for many years manager of the Provincial Bank in Ballymena until murdered (31 May 1889). Hugh attended the Diocesan School, Ballymena, and then TCD, where he won a scholarship before graduating BA in mathematics and philosophy (1882), MA (1885), BD (1888), DD (1897) and D.Litt. (1913). Having been ordained in the Church of Ireland (1886), he served as curate at Christ Church, Kingstown, Co. Dublin (1886–93), and taught at TCD as Archbishop King's lecturer in divinity (1890–93). Lawlor's next appointment was to a senior chaplaincy in the Scottish Episcopal Church at St Mary's, Edinburgh (1893–8), where he was also examining chaplain to the bishop of Edinburgh, John Dowden (qv), a brother of Edward Dowden (qv).
He returned to Ireland to become professor of ecclesiastical history at TCD (1898–1933). As a teacher he was rigorous and once told his class that a clergyman who did not read for six hours each day was unworthy of his post. Lawlor's own reading was extensive – his academic position carried no administrative duties – and resulted in numerous articles and several substantial publications, most notably Chapters on the Book of Mulling (1897), The Reformation and the Irish episcopate (1906), Eusebiana (1912), and The fasti of St Patrick's, Dublin (1930). He edited The Rosslyn Missal, an Irish manuscript in the Advocates' Library, Edinburgh (1899), The diary of William King (1903), The Psalter and Martyrology of Ricemarsh (1914), St Bernard's Life of St Malachy (1920), The ecclesiastical history of Eusebius (with J. E. L. Oulton, 1927–8), The Martyrology of Tallaght (with R. I. Best (qv), 1931) and other documents. He contributed papers on church history and bibliography to the Proceedings of the RIA (most impressively ‘The Cathach of St Columba’ (1916)) and elsewhere. Lawlor was the founder-editor of the Irish Church Quarterly (1908–17). After returning from Scotland he also held positions in the Church of Ireland: he was a curate at Bray, Co. Wicklow (1898–1903), precentor of St Patrick's Cathedral, Dublin (1902–24) and dean (1924–33).
As a clergyman he was well regarded for his learning and preaching. Lawlor was an active member of the RIA (to which he was elected in 1899) and served as secretary of its council (1919–30). Owing to poor health he resigned his deanery and chair and retired to Bray (1933). He died in Dublin on 26 December 1938. He married two first-cousins, Kate Anna Helena or Helen (d. 1903), daughter of Arthur Samuels of Langara, Glenageary, Co. Dublin, and sister of Arthur Warren Samuels (qv), then Leila Mary or Lily (d. 1926), daughter of John Haslar Samuels of Beaufort Lodge, Co. Dublin. The Samuels brothers were joint registrars of the Marriage Licence Office, Dublin. Both marriages were childless. A younger brother of H. J. Lawlor was Henry Cairnes Lawlor (qv), a well-known antiquary.