Fitzgerald, Lord Henry (1761–1829), soldier and politician, was born 30 July 1761, fourth son among nine sons and ten daughters of James Fitzgerald (qv), later 1st duke of Leinster, and his wife Lady Emily Fitzgerald (qv) (née Lennox), daughter of the 2nd duke of Richmond and Lennox. He was educated privately by William Ogilvie (qv), later his step-father, and Dr Thompson. Filled with ideas of military adventure, he entered the army and was a lieutenant in the 66th Foot (1778) and a captain in the 85th Foot (1779), and quickly purchased advancements all the way to lieutenant-colonel (1783). A political liberal, friendly with the prince of Wales, he was brought in by his brother, William Robert Fitzgerald (qv), 2nd duke of Leinster, as MP for Kildare borough (1783–90). At the urging of twenty-three of the twenty-four Dublin guilds he stood for election with Henry Grattan (qv) for Dublin city (1790–97) and both were returned. Although a supporter of the whigs in parliament, he only joined the Whig Club on 7 November 1797. Despite the opposition of Dublin corporation, he voted for catholic relief in 1793.
In May 1798 his brother, Lord Edward Fitzgerald (qv), was arrested for treason after plotting rebellion, and was seriously wounded during his capture. Dying, he requested to see Henry, his favourite brother, who smuggled in letters with the attorney Matthew Dowling (qv). Lord Henry pleaded with the lord chancellor, the earl of Clare (qv), for permission to visit his brother in his final days; but this was refused, and he was only allowed to send strawberries. He was finally permitted to see his brother just before he died.
Disillusioned with politics, and committed to French principles, he went to live in Paris in 1802 after the peace of Amiens. He returned to Ireland before the resumption of war between France and Britain in May 1803, and he also made a return to political life in April 1806 when he was appointed postmaster general for Ireland, after his cousin, Charles James Fox, came into office. In addition, his wife was created Baroness de Ros. On 8 July 1806 he was appointed to the Irish privy council. In 1807 he became an MP for Co. Kildare in the united parliament (1807–14). His contribution was negligible, although when he did vote it was with the opposition. In 1809 he was accepted generally to be the lover of Caroline, princess of Wales, and was suspected of influencing her politically. In November 1810 he was called away to his country estate by the unexpected illness of his wife and children; his son died, and, distraught, he returned all of Caroline's letters and ended the affair. He voted for catholic relief in 1813 but thereafter his appearance in parliament became more infrequent as his health failed. He vacated his seat in February 1814, and was succeeded by his nephew, Lord William Fitzgerald. He retired to Boyle Farm, Kent, where he died on 8 July 1829.
He married (3 August 1791) Charlotte (d. 1831), Baroness de Ros, daughter and heir of Robert Boyle Walsingham, MP; they had six sons and five daughters. The eldest son, Henry William Fitzgerald, succeeded his mother as 22nd Baron de Ros.