MacErlean, John Campbell (Mac Fhir Léinn, Eoin) (1870–1950), Irish-language scholar and church historian, was born 15 February 1870 in Belfast, son of Andrew MacErlean, legal clerk, and Eliza MacErlean (née Campbell). Having attended St Malachy's College, Belfast, he entered the Jesuit novitiate at Tullabeg, King's Co. (1888), and graduated with a BA from the Royal University (1892). After further study on the Continent he returned to Ireland and taught classics and four modern languages (Irish, French, Italian, and German) at Clongowes Wood College, Co. Kildare, for six years. His colleagues at Clongowes included Fr Patrick Dinneen (qv), and MacErlean has been credited with arousing the latter's interest in Irish.
MacErlean showed an interest in Irish as early as 1887 when he collected phrases while on a brief visit to Rathlin Island, although it was not until 1895 that he published this material. He was elected to the Gaelic League's central branch in 1899 and his first scholarly work, an edition of the poetry of Geoffrey Keating (qv), appeared in 1900. After his ordination in 1904 he completed his religious training at Barcelona, where he also acquired a knowledge of Spanish. On his return to Ireland he began to research his most important work, an edition of the poetry of Dáibhí Ó Bruadair (qv) that appeared in three volumes between 1910 and 1917. In the same period he assisted his fellow Jesuit Edmund Hogan (qv) in the preparation of Onomasticon Goedelicum, an index to Irish placenames that was published in 1910. MacErlean was also drawn towards church history: in 1912 he edited seven poems addressed to Eoin Ó Cuileanáin, bishop of Raphoe (1629–c.1658) in the first volume of Archivium Hibernicum; in 1914 his study of the synod of Ráith Bressail, based on the evidence of Keating's Foras feasa ar Éirinn, appeared in the same journal; for many years he was a frequent reviewer of books on church history for Studies; and in 1939 he argued in Analecta Bollandiana that the ‘Silva Focluti’ mentioned in the Confessio of St Patrick (qv) should be identified with modern Magherafelt. Charged by his superiors with the task of collecting materials for a history of the Irish province of the Society of Jesus, he spent two years researching the subject in the archives of Italy, Spain, and Portugal and compiled copious notes, but the history remained unwritten at his death. He also researched the history of the Irish Sisters of Mercy, and the material he collected was used by a biographer of Catherine McAuley (qv).
MacErlean taught theology in the Jesuit novitiate at Milltown Park, Dublin, for twenty-five years and continued to live there until the end of his life. He died in Dublin on 24 March 1950.