He served with the grenadiers in Sicily (1806), at Coruna (1808), on Walcheren (1809), and in Spain and France from 1812 to 1814. In 1815 Lord Saltoun commanded the Light Companies of the First Regiment of Guards (later the Grenadier Guards) in the Orchard at Hougomont on the morning of the Battle of Waterloo; and it was Saltoun who, later in the day, first noticed the Imperial Guard emerge from the hollow where they had been hiding all day, and drew the Duke of Wellington's attention to them. He was appointed a major-general in 1837 and commanded the first brigade in the Battle of Chinkiang (1842) and afterwards the whole force until 1843. He was further promoted to lieutenant-general in 1849.