Gregg, Tresham Dames (1800–81), clergyman and controversialist, was born 11 August 1800 in Dublin, son of Hugh Gregg (c.1775–1805), originally of Dublin but later of Kilkenny, and Martha Gregg (née Dames; 1781–1874). He was a grandson of Tresham Gregg (1751–1809), gaoler of Newgate. After his father's death, his mother married the celebrated mnemonist Gregor von Feinaigle (1765–1819) of Baden, who in 1813 established by public subscription the school that bore his name in Aldborough House, Dublin. Tresham Dames Gregg was educated at the Feinaiglian Institute, where he received a good classical education, including Hebrew. In 1821 he entered TCD as a pensioner, gaining a BA (1826) and an MA (1830). As a young man he was attracted by liberal politics and religious scepticism, but he was ordained deacon in Co. Kilkenny in 1828, and went to work as a curate in Yorkshire, where he took anglican orders in 1830, serving in Earlsheaton, near Dewsbury, and then Sheffield. In 1837, following a profound religious experience, detailed in his work The witness (Sheffield, 1837), he returned to Dublin, convinced that Ireland's various ills stemmed from the prevalence of popery.
Gregg's first post in Dublin (1837–40) was as minister of Swift's Alley Free Church, Francis St., but his views clashed with those of Richard Whately (qv), archbishop of Dublin, who inhibited him from preaching. In 1840 he was elected by the parishioners of St Nicholas Within to the position of chaplain of the chantry of St Mary in the parish chuch of St Nicholas Within. This was a sinecure, but its estate yielded £400 a year, and Gregg held the post till his death. It was still common for clergy to combine a spiritual calling with teaching, and Gregg was headmaster of the Feinaiglian Institute, having inherited the school from his stepfather, till the school closed (possibly owing to Gregg's mismanagement) in 1842.
Gregg came to the attention of the public soon after his return to Dublin, when in late 1837 he gave a lecture at the Merchants' Hall on the union of church and state. His career as a controversialist began in 1838 when, according to Gregg, the Roman catholic protagonist, Fr Thomas Maguire (qv), PP Ballinamore, defied ‘any reverend clergyman out of Trinity’ to overthrow his arguments in defence of the catholic church. Portraying himself as a David taking on Goliath, Gregg accepted the challenge, which led to a public disputation, lasting nine days (29 May–7 June 1838), held in the Rotunda. Gregg's main propositions were that the established church was the true church of Christ in England and Ireland, and that the Roman catholic church was the church of Antichrist. It had been agreed in advance that the proceedings would be published, and the event attracted very large audiences and enormous public interest. With the stakes so high, both sides inevitably claimed victory.
Gregg did not limit his interventions in the protestant cause to the lecture hall. In 1837 he joined the committee of management of the Association for Relief of Distressed Protestants, and in 1840 he published Protestant ascendancy vindicated, addressed to Dublin corporation, which was about to pass from protestant to catholic control following the municipal reform act of 1840. The following year he set up the Dublin Protestant Operative Association, modelled on a pattern already established in England, and soon to be adopted in other Irish towns. The DPOA was intended to boost morale among the still numerous protestant tradesmen, reeling from the twin impact of economic depression and the loss of status following municipal reform. A further significant impetus was the formation (1840) by Daniel O'Connell (qv) of the Loyal National Repeal Association, which solicited support from protestants as well as catholics. The DPOA's overwhelming preoccupation (reflecting Gregg's own convictions) were with the state's apparent indulgence towards popery.
Gregg claimed in 1842 that the DPOA's meetings were regularly attended by 2,000 or more, though it is likely that membership rarely exceeded 500 at any one time. With the reconstitution of the Grand Orange Lodge in 1846 there was less need for operative associations, and the association (which had dropped the word ‘Operative’ from its title in 1845) dissolved itself in May 1848. However, a Dublin Protestant Association, dating from 1841, was still active in the 1860s, with Gregg as one of the vice-presidents. Meanwhile, he published a number of works of scriptural exegesis, including Free thoughts on protestant matters (1845). His reputation as a lecturer in Ireland and England grew.
Through the 1850s Gregg continued to work closely with like-minded clergy and some leading conservatives, including the Dublin city MPs Edward Grogan and John Vance, in support of the union of church and state, and to stress the evils arising, not least to catholics themselves, from state support for popery. This was done through public meetings, lectures, publications, petitions to parliament, and the press. The Dublin Protestant Association, with its organ The Sentinel, was a principal agency for these activities. In 1855 the Sentinel, under Gregg's management, transferred to London, but within two years it had lost money, leaving Gregg (who had taken up a temporary post as minister at St Peter's, Hammersmith) in debt.
Gregg also wrote a series of plays, historical dramas focusing on Tudor monarchs, of which the first was King Edward VI (London, 1857). It is not known whether the plays were ever staged, but they were designed to illustrate the workings of Providence in history, and to challenge the claims of the Roman catholic church to historical legitimacy. In this respect Gregg was influenced by the writings of James Ussher (qv) archbishop of Armagh (1625–56), who had contended that the established Church of Ireland in his own day bore the closest relationship of any contemporary church to that founded by St Patrick in Ireland. During the 1850s the apocalyptic strand in Gregg's thought, always present, intensified, and he became convinced that Armageddon would take place in Ireland (The mystery of God finished (London, 1861)). The disestablishment of the Church of Ireland came as a severe blow to him, and late in life he developed some unorthodox views on the nature of immortality, arguing in A question of universal interest: is death now inevitable? (1879) that extreme longevity, as exemplified in scripture, could be attained as the result of a truly Christian life. He continued to tour and lecture, venturing as far as the USA, into the late 1870s. He also continued a correspondence (commenced in the 1840s) with an increasingly wearied Benjamin Disraeli, in the hope that the latter would adopt Gregg's views on the necessity for the state to support protestantism. Such expectations were repeatedly disappointed, provoking Gregg periodically to anathematise his correspondent; but the hope was never entirely abandoned.
Gregg died at his home in Sandymount, Dublin, on 28 October 1881, and was buried in Mount Jerome cemetery. The eulogy at his funeral was delivered by the Rev. Thomas Mills (1825–1900), the evangelical incumbent of St Jude's, Kilmainham. The Irish Times commented that Gregg had lived and died a poor man, preoccupied as he had been with the cause of protestantism.
Gregg was a man of considerable learning, the author of some twenty-five books. He was particularly proud of his book on Hebrew (A methodization of the Hebrew verbs (London, 1853; 3rd ed., 1861)). His unremitting and fearless defence of the confessional state proved attractive to many protestants, especially in Ireland, faced with the apparently relentless advance of catholicism.
Gregg married (21 December 1832) Sarah Pearson (1814–1902) of Yorkshire; four daughters and three sons survived to adulthood. The eldest son, Tresham Dames Gregg (1842–85), was the chief mourner at his father's funeral.