Spencer, Sir Brent (1760–1828), British army general, was born in Trumery, Co. Antrim, son of Conway Spencer. He was commissioned as an ensign in the 15th Foot in January 1778 and posted to the West Indies, where he took part in the capture of St Lucia. In November 1779 he was promoted to lieutenant and was one of the besieged garrison at Brimstone Hill, St Kitts, which surrendered to the French in February 1782. After a period as a prisoner of war, he was exchanged in 1783 and was promoted to captain in the 99th (Jamaica) Regiment. Transferring back into the 15th Foot, he returned to the West Indies in 1790.
In March 1791 he was promoted to major and, serving with the 13th Foot, took part in the expedition to San Domingo and the capture of Port du Prince. Promoted to lieutenant-colonel in May 1794, he returned to England to command the 115th Foot, and in 1795 returned to the West Indies in command of the 40th Foot. In July 1797 he was promoted to brigadier-general and commanded the troops in the campaign against Toussaint L'Ouverture, the leader of the slave revolt in San Domingo, eventually evacuating the island on the orders of Gen. Maitland. Appointed as an ADC to George III in 1798, he returned to England and then took part in the duke of York's expedition to the Helder (1799). In 1800 he was sent to the Mediterranean and served under Gen. Sir Ralph Abercromby (qv) during the Egyptian expedition, distinguishing himself in the landing at Aboukir Bay (8 March 1801) and in the battle of Alexandria (21 March 1801). His calmness in command under fire was commented upon in the dispatches of both Gen. Sir John Moore (qv) and Abercromby. In April 1801 he captured Rosetta and then Fort St Julien on the western bank of the Nile, and was commended by Abercromby's successor Gen. John Hely-Hutchinson (qv), later Baron Hutchinson.
He returned to England at the end of the Egyptian campaign and was promoted to major-general in January 1805, joining the general staff for the Sussex district. He was appointed as an equerry to George III and soon became a great favourite at court. At this time he embarked on a doomed love affair with Princess Augusta, who pleaded with her father, and later with her brother, the prince of Wales, to be allowed to marry Spencer. Her pleas were refused and there were rumours at court that a secret marriage had taken place between the two lovers. Despite this controversy, he continued to receive promotions and was appointed (1807) to command a brigade in the expedition to Copenhagen. In 1808 he was sent to the Mediterranean with 5,000 men to reinforce Sir Arthur Wellesley (qv) (later duke of Wellington) in the Peninsula. He also carried orders to act as Wellesley's second-in-command – orders that caused some friction between the two men. Wellesley, displaying his characteristic disinclination to delegate command, subjected Spencer to a long harangue, stating that he did not recognise the term ‘second-in-command’ and, indeed, had not asked for one. He later wrote that Spencer had been foisted on him by the government and referred to him as ‘a kind of dry nurse’ (Holmes, Redcoat, 333). Nevertheless, he soon came to appreciate Spencer's coolness in action, and relations between the two men improved.
Spencer was present at the battles of Roliça (17 August) and Vimiera (21 August 1808) and, largely on Wellesley's recommendation, was made a KB in April 1809. After a period of sick-leave in England, he returned to the Peninsula in May 1810, again taking up an appointment as second-in-command to Wellesley (who became Viscount Wellington, 4 September) with the local rank of lieutenant-general. Given command of the first division, he was present at the battles of Busaco (27 September 1810) and Fuentes de Oñoro (3–5 May 1811) and later commanded the British troops in north Portugal, shadowing Marmont's column as it marched southwards to join Soult. Although Wellington was appreciative of Spencer's military ability, he became increasingly irritated with his habit of sending pessimistic letters to friends at court. Wellington was also certain that Spencer had used his recent spell of leave to spread rumours of imminent defeat in the Peninsula. Spencer was promoted to lieutenant-general in June 1811 but relations between the two men became frosty and he obtained leave to go home in July.
For his services in the Peninsula, he received the Peninsular gold medal, with two clasps, and the Portuguese Order of the Tower and Sword. He held the colonelcies of the 9th Garrison Battalion, the 2nd West India Regiment, and the 2nd Battalion of the 95th Rifles, and in 1818 he was made colonel of the 40th Foot. In May 1825 he was promoted to full general on the retired list. He later served on the consolidated board of general officers and as governor of Cork. He died on 29 December 1828 at the Lee, near Great Missenden, Buckinghamshire.
While it is unclear whether Spencer married, the Alumni Cantabrigenses records a Brent Spencer as the only son of Gen. Sir Brent Spencer.