Parnell, Sir Henry Brooke (1776–1842), politician and 1st Baron Congleton , was born 3 July 1776 at Rathleague, Queen's Co. (Laois), second son of Sir John Parnell (qv), Irish MP and chancellor of the exchequer, and Letitia Parnell (née Brooke). In 1789 an act of parliament made him heir to his father's estates as his elder brother, John Augustus, was both mentally and physically disabled. Educated at Eton and Winchester, Henry entered Trinity College, Cambridge (1794), but left without taking a degree. Deciding to join his father in the house of commons, he was returned for Maryborough (1797–1800), and opposed the act of union in the final session of the Irish parliament. He was briefly MP for Queen's Co. and then Portarlington in the united parliament in 1802, but lost both seats. On 17 March 1803 he applied to replace Isaac Corry (qv) as Irish chancellor of the exchequer but, not surprisingly, was rejected, given his inexperience. The following year he published his Observations upon the state of currency in Ireland and its findings were endorsed by a select committee of the house of commons. He returned to parliament in 1806 as MP for Queen's Co., and represented the constituency until 1832; he then took a seat for Dundee (1833–41).
When Lord Grenville (qv) became prime minister in 1806 he appointed Parnell a lord of the Irish treasury. Soon he was defending finance measures in parliament, although he lost office with the change of ministry the following year. In opposition, he attacked the sincerity of the union on 20 April 1807, and was soon speaking in favour of catholic emancipation and tithe reform; he published a History of the penal laws in 1808. His main area of expertise remained finance, and he became a harsh critic of his one-time hero John Foster (qv). Advocating the reform of the relationship between the Irish and British economies, Parnell wanted the currencies united, and argued for the abolition of the Irish lord lieutenancy in 1819, dismissing it as a ‘useless piece of pageantry’. The death of his brother on 30 July 1812 led to his succeeding as 4th baronet. In an important contribution to parliamentary reform in Ireland he was responsible for the 1820 election act that limited polls to fifteen days. He supported Daniel O'Connell (qv) in the campaign for catholic emancipation in the 1820s, and continued to speak in favour of the measure in parliament. With the formation of Lord Grey's whig ministry in 1830 he was appointed secretary at war and became a privy counsellor on 27 April 1831. He was a loner in politics, and his government career was hampered by an inability to work effectively with others. He narrowly escaped dismissal when he encouraged a motion against the post office, but did not learn his lesson and was removed in 1832 for voting against the Russian–Dutch loan. When Lord Melbourne (qv) became prime minister, Parnell was appointed treasurer of the navy on 22 April 1835 and paymaster general of the forces on 14 May. In December 1836 these positions were united, with increased powers, and he became the first holder of the new office of paymaster general.
On 18 August 1841 he was created Baron Congleton of Congleton, Chester, in England. He did not live to enjoy his new title. His health collapsed, and he committed suicide by hanging himself on 8 June 1842 at his home at Cadogan Place, Chelsea, in London. He married (17 February 1801) Caroline Elizabeth Dawson, daughter of the 1st earl of Portarlington; they had three sons and three daughters. His eldest son, John Vesey Parnell (1805–83), succeeded as 2nd Baron Congleton.