General Sir John Alexander Dunlop Agnew Wallace KCB (c.1775 – 11 February 1857) was a British Army officer.

John Alexander Wallace joined the British Army in 1787 as an ensign in the newly raised 75th (Highland) Regiment of Foot.

He served with the regiment in India in 1789, became lieutenant in 1790, and took part in Cornwallis's operations against Sultan Tippoo in 1791–2, including the siege of Seringapatam in 1792.

At the end of 1805, he was transferred to the 88th Regiment of Foot (Connaught Rangers) to command a newly raised second battalion, which was posted to the Peninsular in 1809.

When the French had gained the ridge and seemed to have cut the army in two, a charge made by the 88th, with one wing of the 45th Foot, drove them down headlong.

Picton, who was with another part of his division at the time, gave Wallace the credit of ‘that brilliant exploit.’ He commanded the 88th at the Battle of Fuentes de Oñoro, and was again particularly mentioned in Wellington's despatch.