Lucius Robert O’Brien was born in London on 2 May 1775, baptised at St George’s, Hanover Square on 11 June. He was the 2nd son of Rt Hon Sir Lucius O’Brien 3rd Bt and his wife Anne, daughter of Robert ffrench MP of Monivae Castle, co Galway. He was a cadet in May 1795 and sailed to India on the Woodcot on 18 June 1795, arriving on 30 Oct. He was posted to the 2nd BNC in 1796 and promoted to lieutenant on 1 Nov 1798, appointed Adjutant until 1800 when he was transferred to the 5th BNC as Quartermaster. He was promoted to Captain on 11 Mar 1805 and transferred to the newly raised 8th BNC. On 27 Feb 1812 he was promoted to major and appointed to command the Java Light Cavalry. He was praised by Lt-General Sir Miles Nightingall, the C-in-C in Java, for the high state of discipline of the Java Cavalry, but later was criticised for bullying a junior officer, Cornet Frederick Peret, a married Swiss officer of the 3rd BNC, who was court-martialled, but exonerated and sent back to his regiment.
After the Java Light Cavalry returned to India in 1815, O’Brien was given command of the 8th BNC at Sultanpur, Benares, from 1815 to 1817. In the 3rd Maharatta War he was put in charge of the Guide and Intelligence Department under Brigadier-General Hardyman. He fought at Jubbulpore on 19 Dec 1817 and Mandala in 1818. He was promoted to Lieutenant-Colonel on 26 Feb 1820, commanding the 8th BLC. He was on furlough from 1822 until 5 April 1825. On 23 July 1823 he was appointed CB, and in 1824 he was transferred to the 6th BLC in May, then to the 4th BLC in October. But he died of cholera at Sultanpur on 10 July 1825. He was married to Julia Humphreys of Dublin on 6 Jan 1824. They had a son, William.
