Irish architect, probably from Co. Cork. He carried out numerous works for the ‘edifying’ Frederick Augustus Hervey (1730–1803), Bishop of Derry and Earl of Bristol. He appears to have been involved in the design and construction of Downhill, the Bishop's great house in Co. Londonderry (begun c.1775—un-roofed 1950, and now a shell), although James Wyatt may have produced drawings for it (and there are certain features, such as the attenuated pilasters, which look very much like Wyatt's work). His masterpiece is the domed circular Mussenden Temple (1783–5) on a headland at Downhill, high above the sea: a distinguished design, it is based on Roman exemplars. He was also responsible for the ‘mausoleum’ (actually a memorial) at Downhill (begun 1779), which is modelled on the Roman mausoleum of the Julii, St-Rémy, Provence: the upper parts of this charming building were blown down in the ‘Great Wind’ of 1839. He may also have designed the Bishop and Lion Gates at Downhill (1784 and 1778–9), both of which have Wyattesque touches. Shanahan probably designed and directed the building of several Anglican churches in the Diocese of Derry (e.g. Desertoghill, near Garvagh, and Banagher (1775–6) ).