Gwynn, John (1827–1917), clergyman and scholar, was born 28 August 1827 in Larne, Co. Antrim, eldest son among four sons and two daughters of the Rev. Stephen Gwynne, rector of Agherton, Co. Londonderry, and Mary Gwynne (née Stevens or Stevenson). Their mother drowned at Portstewart in October 1837 when the youngest child was only 4 years old; the father married again in January 1841. John (who may have been the first of his family to use the spelling ‘Gwynn’) was educated by his father and at the Royal School (Portora), Enniskillen, and entered TCD 6 November 1845. He became a scholar (1848), graduated BA (1850), and was a fellow 1853–64; he was warden of St Columba's College, Rathfarnham, Co. Dublin, from 1856 to 1864, when he resigned his fellowship on being granted the college living of Tullyaughnish, Co. Donegal. He was rector there till 1882, dean of Raphoe 1873–82, and rector of Templemore and dean of Derry 1882–3.
Gwynn was prominent in discussions concerning the disestablishment of the Church of Ireland, but was most notable as a scholar. In 1883 he became Archbishop King's lecturer in divinity in TCD; in 1888 he was chosen regius professor of divinity. He became an expert on Syriac, which he had first studied to pass the time on long train journeys from Strabane to Dublin; in 1893 he published memoirs on Syriac versions of the New Testament, and in 1897 he edited a hitherto unknown Syriac text of St John's Apocalypse. Scholarly papers appeared in journals such as Hermathena and the Church Quarterly Review, and he wrote over thirty articles in the Dictionary of Christian biography, as well as translations, sermons, and pamphlets. After many years of study, he published in 1913 an important edition of the ninth-century Book of Armagh, still highly regarded at the beginning of the twenty-first century. In 1861 Gwynn received a BD degree (Dubl.), in 1880 he was made DD, and in 1892 was awarded the honorary degree of DCL by Oxford University.
He married (26 June 1862) Lucy Josephine (d. 1907), eldest daughter of William Smith O'Brien (qv). Their eight sons and two daughters included Stephen L. Gwynn (qv), Lucius H. Gwynn (qv), Edward J. Gwynn (qv), Charles W. Gwynn, Robert Malcolm Gwynn (1877–1962), professor of Hebrew at TCD, John Tudor Gwynn (1881–1956), Irish correspondent of the Manchester Guardian 1923–36, Brian James Gwynn (1888–1972), civil servant in Ireland, and Arthur Percival Gwynn (1874–97), who played rugby for Ireland and died in Burma. Lucy Penelope Gwynn (1866–1947) was the first lady registrar of TCD (1905–15).