Trench, William Le Poer (1837–1920), soldier and MP, was born 17 June 1837 at Garbally, Ballinasloe, Co. Galway, third son of William Thomas Le Poer Trench, 3rd earl of Clancarty, and his wife Lady Sarah Juliana, daughter of Somerset Richard Butler, 3rd earl of Carrick. After attending Cheltenham College, he entered the Royal Military Academy at Woolwich, being commissioned as a second lieutenant in the Royal Engineers in October 1854. He was promoted to lieutenant (January 1855) and served in the second China war (the ‘Arrow war’, 1857–60), taking part in the preparations for the storming of Canton (December 1857) where he commanded a ladder party in the assault. He also commanded a ladder party in the storming of Namtow and was mentioned in despatches and awarded the Second China War Medal. In 1861 he was appointed to a European survey project, commanding the British contingent in the operations to connect the triangulation of England with Germany through France and Belgium. He was promoted to captain (October 1861) and later to major (July 1872).
In February 1872 he stood as the tory candidate in the Co. Galway by-election and was decisively beaten by Capt. John Philip Nolan (qv), a home rule candidate, who secured 2,823 votes to Trench's 658. Trench lodged a petition, however, complaining that the local clergy had improperly influenced the electorate. The petition was tried by Judge William Nicholas Keogh (qv), who found in Trench's favour and energetically denounced the local clergy as part of his summation. As a result of this successful petition, Nolan was unseated in June 1872 and Trench was declared to be elected. He did not contest the seat in the 1874 election, however, and Nolan was again elected by a clear majority. During his short career as an MP Trench spoke in the commons in support of denominational education, also proposing a series of public works schemes to develop the resources of Ireland.
In 1877–9 he served as chairman of the poor law and lunacy inquiry commission and was promoted to lieutenant-colonel (October 1879) and colonel (November 1879) on the retired list. He stood unsuccessfully as a tory candidate in elections in Whitechapel (1886, 1893) and served as a JP for London, Westminster, Middlesex, and Buckinghamshire. A member of the Carlton, Constitutional, and United Services clubs, he died 16 September 1920 at his residence, St Hubert's, Gerrard's Cross, Bucks.
He married (April 1864) Harriet Maria Georgina (d. 1909), only daughter and heir of Sir William Martins. They had two sons.