He was commissioned as an ensign and lieutenant in the 1st Foot Guards then promoted to lieutenant and captain on 12November 1807. Trench served on the quartermaster's staff in Sicily in 1806-7 and was part of the disastrous 1809 Walcheren Expedition. He was sent to Cadiz in 1811 during the Peninsular War until on 1August he was promoted to major and appointed assistant quartermaster-general in the Kent district. After his appoint as deputy quartermaster-general to the corps on 25November 1813, he accompanied General Sir Thomas Graham to Holland in 1814 as a lieutenant-colonel. In 1814 he was placed on half-pay and became an "aide-de-camp" to the King on 27May 1825. Under the Wellington ministry he was appointed Storekeeper of the Ordnance in 1829, a post he held until 1831. He was promoted to general in 1846.