Campbell was posted to Gibraltar in 1810 and fought at the Battle of Barrosa in March 1811, taking command of the 9th Foot's flank companies as the senior officer not "hors de combat". His bravery was noted by General Sir Thomas Graham. Serving in his battalion's light company, he fought at the Battle of Vitoria in June 1813 and at the Siege of San Sebastián. Here, in the first assault on 25 July 1813, he led the forlorn hope and was wounded twice while leading a storming party. He led the 9th Foot's light company at the Battle of the Bidassoa in October 1813 where he was wounded for the third time. He was promoted to captain in the 7th Battalion 60th (Royal American) Regiment on 3 November 1813. Sent to Halifax, Nova Scotia, he was too late to see action in the War of 1812 and soon returned to Europe suffering from his wounds. Due to the contraction of the army after Waterloo the number of Royal American battalions was cut back drastically. To avoid being put on half-pay Campbell transferred to the 21st Royal North British Fusiliers on 26 November 1818. The regiment was sent first to Barbados and then to Demerara, where Campbell became aide-de-camp to the governor. His part in quelling the slave rebellion in Demerara in August 1823 is hazy. He is not recorded as joining in the reprisals against slaves pursued by his commanding officer, Lieutenant-Colonel Leahy, but he was on the court-martial which sentenced Reverend John Smith, the suspected instigator of the revolt, to death. He purchased his majority on 26 November 1825.