Leslie, James Blennerhassett (1865–1952), clergyman and scholar, was born 28 May 1865, third son of James Leslie, farmer, and Mary Anne Leslie (née Blennerhassett) of Clouncannon, Killarney, Co. Kerry. He read history, political economy, and jurisprudence at QCC (BA 1888, MA 1889), and obtained a first-class divinity testimonium from TCD prior to ordination in the Church of Ireland as a deacon (1891) and priest (1892). He served as curate at Christ Church, Belfast (1891–4) and at Portadown (1894–9). He was appointed (1891) rector of Kilsaran, a light-duty parish in Co. Louth in the diocese of Armagh, and remained there until his retirement in 1951, when he moved to Dublin. He was prebendary of Mullabrack (1925–8), treasurer (1928–34) and chancellor (1934–43), all in Armagh cathedral, and prebendary of Yagoe in St Patrick's cathedral, Dublin (1943–51). He was awarded D.Litt. from QUB in 1931.
He devoted much of his life to historical research, beginning with The mission of Patrick: was it from Rome? (1901) and The history of the union of Kilsaran (1908). His main scholarly work was in compiling biographical succession lists for the dioceses of the Church of Ireland. These lists contain personal and professional details of the Church of Ireland clergy and, for the period before the reformation, of the clergy of the church in Ireland, and were compiled as separate volumes for each diocese. Each volume contains succession lists of bishops, cathedral clergy, and parish clergy, arranged chronologically according to the date of appointment. The main part of each volume contains the biographies of the clergy. In addition there is sometimes information on the history of church buildings and parishes. He published eight volumes of diocesan succession lists and left nineteen volumes of unpublished typescripts which dealt with seventeen dioceses and Christ Church cathedral, Dublin. Lack of finance seems to have been the main limiting factor in publishing the lists. The published volumes are Armagh clergy and parishes (1911), Clogher clergy and parishes (1929), Ossory clergy and parishes (1933), Ferns clergy and parishes (1936), Derry clergy and parishes (1937), Ardfert and Aghadoe clergy and parishes (1940), Raphoe clergy and parishes (1940), and Supplement to Armagh clergy and parishes (1948). The copyright of the unpublished lists is held by the library of the Representative Church Body in Dublin. He was editor of the Irish Clergy List (1910) and of the Irish Church Directory (1928–40), and was the first hon. secretary of the ecclesiastical records committee of the Church of Ireland. He calendared and edited the correspondence of Lord John George Beresford (qv) and the miscellaneous MSS in the Armagh registry. Leslie died 20 April 1952 in Dublin.
He married (9 August 1893) Mary, eldest daughter of William Bulfin of Dublin; they had two daughters, both of whom died unmarried.