Gregg, John (1798–1878), Church of Ireland bishop, was born 4 August 1798 at Cappa, near Ennis, Co. Clare, fifth son and twelfth and youngest surviving child of Richard Gregg (1742–1808), country gentleman, and Barbara Gregg (née Fitzgerald), a catholic and sister of James Fitzgerald (qv) (1742–1835). On his father's death, he was aged nine; he later described himself as ‘the orphan child of the only protestant family in one of the obscurest parishes in the most neglected county in Ireland’ (Gregg, 15). He was educated at a classical school in Ennis and, winning a sizarship, entered TCD (1819) and graduated BA (1824), MA, BD, and DD (1860). As a student listening to a sermon preached by the Rev. B. W. Matthias (1772–1841), he ‘caught the spark that set my soul on fire’ (Gregg, 12), and was ordained in 1826 and appointed curate of the French church, Portarlington, Queen's Co. (Laois) (1826–8) and vicar at Kilsallaghan, Co. Dublin (1828–35).
A leading member of the evangelical movement, and an eloquent preacher, he converted his mother to protestantism and travelled on Church Home Mission tours to every county in Ireland, often speaking in Irish, as on the occasion when he preached to catholics in St Nicholas's, Galway, and to Irish catholic congregations in Liverpool and London. His friendliness and humour won him the affection of catholics, and throughout the tithe war of the 1830s he received his dues. As chaplain of the Bethesda chapel, Dublin (1835–9), his congregation was so numerous that he was given a donation to build a larger church. The new building, Trinity Church, Lower Gardiner St. (consecrated 1839), attracted congregations of 2,000, including students from TCD, among them J. P. Mahaffy (qv) and W. E. H. Lecky (qv). Gregg was considered the greatest preacher of his age, and his hour-long extempore sermons reflected his deep concentration on the text, wide learning, and earnestness. He was known as ‘good John Gregg’, and his work among the poor and his addresses to children were striking features of his pastorate. He never engaged in church politics or secular affairs and refused offers of preferment, but accepted the additional office of archdeacon of Kildare (1857–62).
In 1862 he was appointed bishop of Cork, Cloyne, and Ross, becoming the first Irish-speaking bishop since William Bedell (qv). His episcopate coincided with the disestablishment of the church and he helped in its reorganisation and in the revision of the Prayer Book, but was unsympathetic to ritual or doctrinal change. It was also marked by the building of St Fin Barre's cathedral. The design by William Burges (qv) of a neo-Gothic cathedral, though costing twice the prescribed sum of £15,000, was accepted and Gregg laid the foundation stone in 1865. The construction of this remarkable building became his great ambition and with each redrawing of the plans it became ever more lavish; winning the affection of the people, appealing to religious rivalry and civic pride. His fund-raising was extraordinarily effective, and though costs rose to £100,000 his dream of a cathedral to ‘strike the human mind with its sublimity’ (Crook, 207) was fulfilled with its trinity of towers and central spire soaring to 240 ft (73 m). Gregg ceremonially laid the top-stone on one of the western spires on 6 April 1878 – his last public appearance before his death. His published works include A missionary visit to Achill and Erris (3rd ed. 1850) and many tracts, lectures, and sermons – some collected and published by his son Robert as The life of faith: sermons and lectures (1883–5) – and The story of stories and other sermons to children (1879). He died 26 May 1878 at the Palace, Cork, and was buried in Mount Jerome cemetery, Dublin. His eldest son erected the memorial altar of carved oak, resting on black marble, inlaid with mosaic in the cathedral.
He married (1830) Elizabeth Nicola, daughter of Robert Law of Finlay's Bank, Dublin; they had three sons and three daughters. Their eldest son, John Robert Gregg (1831–82), became vicar at Deptford, Kent, England, and the youngest son, John Allen Fitzgerald Gregg (qv), became archbishop of Dublin. The second son, Robert Samuel Gregg (qv), succeeded his father as bishop of Cork, subsequently becoming archbishop of Armagh (1893), and wrote Memorials of the life of John Gregg, D.D. (1879).