Dickson entered the Royal Military Academy in 1793, passing out as second lieutenant in the Royal Artillery in the following year. As a subaltern he saw service in Menorca in 1798 and at Malta in 1800. As a captain he took part in the unfortunate Montevideo Expedition of 1806–07, and in 1809 he accompanied Brigadier General Edward Howorth to Portugal where he served as brigade-major of the artillery.[2]
He soon obtained a command in the Portuguese artillery, and as a lieutenant colonel of the Portuguese service took part in the various battles of 1810–11. At the sieges of Ciudad Rodrigo, Badajoz, the Salamanca forts, and Burgos, he was entrusted by Wellington with most of the detailed artillery work. At the Battle of Salamanca he commanded the reserve artillery. In the end he became commander of the whole of the artillery of the allied army, and though still only a substantive captain in the British service, he had under his orders some 8000 men. He played a key role in the successful conclusion of the Siege of San Sebastián in 1813. At the battles of Vitoria, the Pyrenees and Toulouse he directed the movements of the artillery engaged, and at the end of the war received handsome presents from the officers who had served under him, many of whom were his seniors in the army list.[2]
He was at the disastrous Battle of New Orleans, but returned to Europe in time for the Waterloo campaign. He was present at Quatre Bras and Waterloo on the artillery staff of Wellington's army, and subsequently commanded the British battering train at the sieges of the French fortresses left behind the advancing allies. For the rest of his life he was on home service, principally as a staff officer of artillery[2] with the rank of major general and title of Master Gunner St James's Park.[3]
Leslie, John H., ed. (1987) [1905]. The Dickson manuscripts : being diaries, letters, maps, account books, with various other papers of the late Major-General Sir Alexander Dickson [1809-1813]. Cambridge: Ken Trotman. ISBN978-0-94-687922-9.
Lipscombe, Nick (2013). "Dickson, the Die is Cast - Chapter 12". Wellington's Guns - The Untold Story of Wellington and his Artillery in the Peninsula and at Waterloo. Oxford: Osprey Publishing. doi:10.5040/9781472896001.ch-012. ISBN978-1-78-096114-9.