Duff, Thomas (c.1792–1848), architect, was born in Newry, Co. Down. Nothing is known of his parentage and early life, except that he was a catholic. It is possible that he was the ‘Thomas Duffe’ who won a prize at the Dublin Society (1805) for an architectural design. It is not clear where he trained as an architect but his unusually strong grasp of the latest variations in neo-Grecian, Roman, and Gothic styles suggests that he visited England. In addition he kept abreast of new tastes by subscribing to numerous architectural pattern books. As early as 1813 he may have worked, in a supervisory capacity, on the construction of St Mary's (catholic) church, Newry. Stylistic evidence suggests that he also had a hand in the design of Armagh courthouse (1815), Kilkeel (Church of Ireland) church (1815), and Rostrevor (Church of Ireland) church (1818). He was well established by the early 1820s and had set up offices at College Square, Belfast, as well as in Newry. An advertisement in a Belfast newspaper in 1822 refers to ‘Mr Duff who for several succeeding years has been engaged making architectural designs and estimates’ (Belfast News Letter, 22 November 1822).
In 1824 he landed his first major commission: to design the presbyterian church on Fisherwick Place, Belfast. This was an outstanding neo-Grecian building with a prominent portico with columns of the Ionic order (since demolished), and at the time was the grandest presbyterian church in Ireland. While Fisherwick Place was under construction he was engaged in designing an equally important building but in a completely different style: the catholic cathedral of SS Patrick and Colman, Newry. When completed in 1829 it was the first large-scale Gothic-revival catholic church in Ireland. Though much altered and enlarged since then, Duff's brilliant handling of the Perpendicular Gothic style (a light and airy space achieved by a lofty arcade, graceful columns, and large windows) can still be observed. The popularity of his cathedral design, and the fact that he was cheaper to employ than English architects, won him a number of commissions to build a plethora of smaller churches and chapels in Ulster. Among those that can be attributed to him (or his followers) in the 1820s are the presbyterian churches at Portaferry, Antrim, and Newry (Sandys St.); Ardee catholic church; Kircubbin anglican church; and the Ebenezer nonconformist chapel, Newry.
He was a truly universal architect and could turn his hand to practically anything, including municipal buildings and country houses. Though he was a catholic, his status as one of the few professional architects in Ulster meant that a number of protestant grandees were prepared to employ him. In the mid to late 1820s he was engaged by the 3rd marquis of Downshire (qv) to design the corn market and session house at Edenderry, King's Co. (Offaly), Hilltown market house, and Dundrum inn and baths. He also made proposals for the house and church at Loughbrickland (all in Co. Down). For relatively little outlay – Duff was typically paid around £50 for a set of court house designs – his Ulster patrons could obtain decent buildings for a fraction of the cost of employing a London-based architect.
In about 1830 he formed a partnership with another up and coming Ulster architect, Thomas Jackson (qv). Their first major joint commission was the Belfast Natural History and Philosophical Society building, Belfast. With quite a narrow site they were able to create an elegant neo-Grecian façade with pilasters and pediment completely in keeping with the grandeur of the adjacent Academical Institution. The partnership ended in 1835 when Jackson set up his own practice. Duff worked for a number of prominent landowners in Ulster during the 1830s but was unable to clinch commissions to design entirely new seats. The gate lodges at the Argory, Co. Armagh (c.1835) and Donard Lodge, Co. Down (c.1836) are attributed to him and he is known to have made modifications and additions to Caledon, Co. Tyrone; he also designed a monumental column for the grounds. His design for Narrow Water Castle, Co. Down (completed c.1837), an imposing Tudor-revival house which encased an earlier building with a fairy-tale profusion of oriel windows, towers, and pinnacles, shows that he was able to master designs from the very latest pattern books. Large sections of two other large houses – Parkanaur, a sprawling Tudor pile (Co. Tyrone), and Ravensdale, a classical mansion (Co. Louth) – were remodelled by him. He also provided classical designs for a number of institutions such as Newry courthouse (1837–41) and possibly St Macartan's seminary, Co. Monaghan (1840–48).
Perhaps the crowning achievement of his career was the church of St Patrick (the catholic pro-cathedral) in Dundalk (begun 1837; completed 1842). Like Newry cathedral, the design is based on the best examples of English Perpendicular architecture such as King's College chapel, Cambridge, and Bath abbey. The long rectangular nave with its graceful columns is perfectly symmetrical, with lean-to aisles and octagonal turrets in each corner (the Tudor-style screen, some of the internal fittings, and the adjacent free-standing belfry are by later architects). By the late 1830s he was seen as the foremost ecclesiastical architect working in Ireland and in 1840 he was asked to design the most important Roman catholic church in Ireland, the cathedral of St Patrick in Armagh. He envisaged a magnificent cruciform edifice with a large-scale tower over the crossing and twin towers at the west end. Foundations were laid during the early 1840s but work stopped as a result of the famine. By the time work resumed in the early 1850s, Duff was dead and the work was taken over by J. J. McCarthy (qv), who was given permission by the church authorities to make radical alterations to Duff's designs, using the early Gothic style.
Duff was the most important architect working in Ulster in the period c.1825–45. The quality of his work encouraged ecclesiastical and landed patrons to look again at home-grown talent rather than automatically select more expensive architects in England. His late Gothic/Perpendicular gabled-hall church designs, such as Newry and Dundalk, could be scaled down to suit every denomination from the large catholic churches to the smallest nonconformist chapel. Many of the churches built in Ulster before the great famine are greatly influenced by Duff (such as St Malachy's Church, Belfast, designed by Thomas Jackson (qv)). Duff had at least one apprentice, William Barre (qv), who also became a successful architect. His later personal life was filled with tragedy. In June 1847 his only son Roger died aged 14. While he was still trying to come to terms with this loss, one of his daughters died (7 May 1848). Three days later Thomas Duff died, as a result of a stroke, aged 56. He was survived by his wife, Jane (maiden name and date of marriage unknown), and three young daughters.