Mahony, Pierce (1792–1853), solicitor, was born 19 December 1792, probably in Co. Kerry, son of Pierce Mahony (1750–1819), landowner and JP of Co. Kerry and Co. Limerick, and his second wife, Anna Maria, daughter of John Maunsell of Ballybrood House, Co. Limerick. The protestant Mahonys were an old Kerry family who counted among their ancestors a number of high sheriffs of the county. Pierce established himself as a solicitor, setting up with his brother David (1795–1844) the firm Pierce and David Mahony & Co. at 22–3 William St., Dublin, which built up a substantial practice as solicitors to five major insurance companies. The brothers were also considerable shareholders in numerous concerns and Pierce maintained establishments in Stillorgan, Co. Dublin, and at the family estate of Woodlawn, Killarney. In 1828 Daniel O'Connell (qv) appointed him his parliamentary agent and was soon declaring him ‘the best I ever knew . . . he has carried more difficult acts of parliament than any other Irish or English solicitor ever did . . . he knows all the members as well as all the ways of the house’ (O'Connell, Corr., iii, 413). Mahony, who was known in Dublin as ‘the prince of attorneys’, acted as agent throughout the passing of the emancipation act (April 1829). This met all his political requirements and when O'Connell sought to go further, the protestant Mahony ceased to work for him and became an active anti-repealer. In 1830 he drew up a declaration which bound its signatories to preserving the British connection, and he had the duke of Leinster (qv) launch it at a meeting in Dublin on 29 October 1830. This became known as the ‘Leinster declaration’, eventually signed by some seventy-five peers and twenty-three MPs as well as numerous others. When Mahony presented himself for election in the liberal interest in Limerick in October 1832, O'Connell denounced him as the ‘prince of political jobbers . . . who came in at the fag end of emancipation’ (O'Connell, Corr., iv, 462). Mahony withdrew and so won back O'Connell's friendship. By the following September O'Connell was supporting, through an article in the Pilot, Mahony's candidature for solicitor of the ecclesiastical commissioners for Ireland, though in the event he was not appointed. Within five years Mahony had come sufficiently round to O'Connell's thinking to stand as repeal candidate for Kinsale, Co. Cork, in the general election of 1837. He was elected by 103 votes to 98 for the sitting conservative member, Henry Thomas, but was unseated on petition, Thomas being declared elected on 11 April 1838. During the state trials of 1844 Mahony acted as attorney to O'Connell and the traversers, and in this capacity queried the special jury list, which included only twenty-three catholics. His last service for O'Connell was in drawing up in October 1844 a declaration in favour of federalism, which did not, however, have the impact of the Leinster declaration.
He was clerk of the queen's bench, Ireland, from 1849 until his death on 18 February 1853. He was survived by his wife (m. 10 January 1815), Jane (née Kenifeck) of Seafort, Co. Cork, and by a son and a daughter. His son, Pierce Mahony (1817–50), high sheriff of Kerry in 1844, predeceased him by three years. A bust of Pierce Mahony by John Edward Jones (qv) is in the Stephen's Green Club, Dublin, of which he was an original member.