In 1806, at the head of his regiment he joined Sir David Baird's expedition to the Cape of Good Hope and on 8 January was wounded in action against the Batavian army at the Battle of Blaauwberg.

On announcing the victory of the British in despatches Baird remarked: "Your lordship will perceive the name of Lt.-Col. Grant among the wounded; but the heroic spirit of this officer was not subdued by his misfortune, and he continued to lead his men to glory as long as an enemy was opposed to the 72nd Regt.

"[2]He exchanged to the 15th Hussars in 1808, and took part in Sir John Moore's expedition to the Peninsular, being wounded at Sahagún fighting the French.

However, Grant's political influence meant that he soon returned to the Peninsular to take over command of the light dragoon brigade of Robert Ballard Long.

At Waterloo, Grant commanded the 5th Cavalry Brigade, consisting of the 7th and 15th Hussars with the 13th Light Dragoons attached, which was stationed in the centre of the allied position; during the battle he had five horses shot under him.