Fitzgerald, Augustus Frederick (1791–1874), 3rd duke of Leinster , grand master of the freemasons of Ireland, was born 21 August 1791 at Carton, Co. Kildare, eldest child of William Robert Fitzgerald (1748–1804), 2nd duke of Leinster, and his wife, Emilia Olivia, daughter of the 1st Baron St George of Hatley St George. His paternal grandmother was Emily (qv), duchess of Leinster, and his uncle was Lord Edward Fitzgerald (qv). He received his Teutonic forenames from his godfather, the prince of Wales, and succeeded to the dukedom at the age of 13. Educated at Eton and Oxford, he matriculated in October 1810 but did not graduate. On attaining his majority he took his seat in the house of lords in 1813, and that year was also appointed grand master of the freemasons of Ireland (1813–74).
He steered a careful line between loyalty to the crown and to the Masonic order, which during the 1820s and 1830s was in danger of being penalised under the laws prohibiting secret societies in Ireland. Leinster complied with the restrictions, directing that no Irish lodge should assemble as of 1 August 1823, while successfully using his influence to end the prohibition in June 1824. A parliamentary prohibition (1836) of all public processions had a more lasting effect on the order; since 21 June 1836 Masonic processions have only been allowed by dispensation from the grand lodge, and this has rarely been granted. Leinster also centralised the previously disparate order and in 1844 established the principle that lodges could only exist by warrant. His last service to the order was in persuading the prince of Wales to become its patron in 1871.
In the lords he upheld the whig traditions of his family, and was an early supporter of catholic emancipation; his was one of the twelve signatures to the requisition to the lord mayor of Dublin in favour of a protestant meeting for emancipation (11 February 1819). He was subsequently one of sixty-five protestant peers to advocate emancipation after the lords' rejection of the catholic relief bill (27 June 1825), and himself presented a petition to the king in 1829. However, by this date Daniel O'Connell (qv) had become disillusioned by his ‘paltry declarations – just enough to serve as an excuse for doing nothing’ (O'Connell corr., iii, 404). The divisions between the two widened in the 1830s: Leinster was no repealer and on 29 October 1830 drew up the ‘Leinster declaration’ in support of the union; by December seventy-five peers and twenty-three MPs had signed, causing O'Connell to denounce that ‘most miserable of miserable dukes’ (ibid., iv, 221). Although Leinster remained sympathetic within the confines of his unionism, and supported the Irish juries bill (1832), he resisted O'Connell's attempts in 1834 to bring him into an anti-tory alliance of repealers and whigs, and in June 1841 refused to allow his eldest son to stand as a liberal for Dublin. By 1844 his name to O'Connell ‘operated like vomit’ (ibid., vii, 3073).
Leinster's other political interest was education, though here again he avoided playing a leading role. In 1815 he agreed to be patron and subscriber of the Society for Promoting the Education of the Poor in Ireland, better known as the Kildare Place Society. Through O'Connell's influence, he became convinced by 1819 that by its rigid emphasis on scriptural readings the society was proselytising. However, he refused to go as far in outright public condemnation as O'Connell wished, contenting himself with criticisms in the lords. His goodwill made him a natural choice for those in government seeking an influential figurehead for the movement for non-denominational schools. In a famous letter printed in the Dublin Gazette (8 Dec. 1831) the chief secretary, Lord Stanley (qv), laid out to Leinster his proposals for a new board of education, which were subsequently implemented, with the duke being appointed first commissioner of the board in 1836 (though he remained largely a figurehead).
Leinster resigned as commissioner on 31 December 1840, pleading duties as magistrate and poor law guardian. The latter became more onerous in the course of the decade. He was a member of the Mansion House committee (21 October 1845) on the causes of the potato failure, and advised limiting food exports. Subsequently he spoke in favour of the treasury's policy of enforcing payment of poor rates, though other landlords complained that he was only supportive because he had in Celbridge the best situated union in Ireland. His record as a landlord has traditionally been represented as exemplary; he is one of the few whom Cecil Woodham Smith commends, and he was referred to affectionately as ‘the good, old duke of Leinster, the most liberal and generous of landlords’ (Macaulay, 279). However, a recent study indicates more widespread poverty in Kildare than was previously admitted, and points to large-scale land clearances in Athy during the famine. In later years the reputations of the duke and his successor suffered from the enactment of the 1870 land act. The ‘Leinster lease’, which required tenants to relinquish claims to compensation, became infamous for its stringency and was ceremoniously burned in 1881 at a Land League meeting in the marketplace of Athy.
Leinster died at Carton on 10 October 1874. He married (16 June 1818) Charlotte Augusta Stanhope (d. 15 February 1859), daughter of the 3rd earl of Harrington, and was survived by three sons and a daughter. His eldest son, Charles William Fitzgerald (1819–87), 4th duke of Leinster, was commissioner for national education 1841–87, where his most significant action was to move, in accordance with the catholic bishops' demands, the 1866 resolution stating that catholic children should not attend protestant religious instruction, nor vice versa. His younger son, Lord Otho Augustus Fitzgerald (1827–82), was liberal MP for Kildare (1865–74).