Ashlin, George Coppinger (1837–1921), architect, was born 28 May 1837 at Carrigrenane House, Co. Cork, third and youngest son of four children of John Musson Ashlin, a Corkman established as a corn merchant in London, and Dorinda Maria Ashlin (née Coppinger), from an old Co. Cork family. The family lived in London, and Ashlin was educated at the College of St Servais, Liège, Belgium; St Mary's College, Oscott, Birmingham (1851–5); and the Royal Academy, London (1859). In 1856 he was apprenticed to Edward Welby Pugin (qv) (1834–75), who in 1860 won the competition to build the Church of SS Peter & Paul, Cork, and offered Ashlin a partnership in the practice with responsibility for opening a Dublin branch to take charge of Irish commissions. Thus Ashlin inherited the Gothic style of his partner's eminent father, Augustus W. N. Pugin (qv) (1812–52). In an era of great expansion in catholic church-building, Ashlin became a leading ecclesiastical architect, designing, altering, and completing at least sixty churches and cathedrals throughout the country, as well as schools and convents. For many years ‘Pugin & Ashlin’ were synonymous with church-building; their most elaborate church, built in French Gothic style, was SS Augustine and John, Thomas St., Dublin (1860). Their masterpiece, begun in 1868, was St Colman's cathedral, Cobh, Co. Cork; built on a hill overlooking the harbour, its spire rising to a height of 300 ft (91.44 m), it was completed by Ashlin and Coleman in 1919. For reasons unknown, Ashlin's partnership with Pugin ended in 1868 and he practised independently until 1902, when he invited a former pupil, Thomas Aloysius Coleman (1865–1950) into partnership.
Under the influence of the Celtic revival, Ashlin turned to ancient Irish architecture for inspiration. In 1877 he designed a domestic chapel for A. J. Moore of Mooresfort, Co. Tipperary, which was modelled on Cormac's Chapel, Cashel, Co. Tipperary. This was an early example of Hiberno-Romanesque, which was to become the dominant style in Irish catholic church design. The Daniel O'Connell (qv) memorial church, Cahirciveen, Co. Kerry (1884), in French Gothic idiom, has an ‘Irish character’, as has the McCabe memorial in Glasnevin cemetery, Dublin (1887), with its ‘riot of Hiberno-Romanesque decoration’ (de Breffny, 37). In his presidential address to the Royal Institute of Architects in Ireland, ‘The possibility of the revival of the ancient arts of Ireland and their adaptation to modern circumstances’ (1902), Ashlin expressed the hope that the institute would encourage a national style, reflecting present ideals, using modern materials but inspired by ancient Irish architecture. Ashlin's secular buildings include the Exhibition of Irish Arts and Manufactures (1882); commercial offices in Dublin; Tulira Castle, Co. Galway (1880), for Edward Martyn (qv); and notably, Portrane asylum, Dublin – begun in 1896, costing over £300,000, it was then the most expensive secular building ever undertaken in Ireland. Ashlin was a member of the RHA and AAI, FRIBA, and fellow (1863), council member (1864–6, 1870–74, 1876–1901) and president (1902–4) of the RIAI. He married (1867) Mary, E. W. Pugin's sister; their only child, Miriam, married her cousin Stephen Martin Ashlin, who continued the firm of Ashlin & Coleman after Ashlin's death. Ashlin died 10 December 1921 at his red-brick Gothic residence, St George's, Killiney, Co. Dublin, which he built after the birth of his daughter in 1877.