Cameron joined the army in the Peninsular in late 1808, as a Brigadier-General commanding the 2nd Brigade of Rowland Hill’s 3rd Division in Portugal, collecting stragglers from Moore’s army. Under Wellesley from 1809, his brigade saw action at Oporto 12 May, then became the 2nd Brigade of Sherbrooke’s 1st Division, fighting at Talavera 28 July, and at Busaco 27 September 1810. He was promoted Major-General on 25 July 1810 and invalided home.