He participated first in the expedition of Portugal led by General Junot, where he took part in the battle of Vimeiro, then in Spain, under the orders of his brother General Horace Sébastiani (1809–1811), where he distinguished in the battles of Ciudad Real, Santa-Cruz, Talaveira, Almonacid, in the passage of the Sierra Morena (where he was elevated to the rank of Knight of the Legion of Honour on 23 June 1810) and in the take of Malaga. He received command of mobile columns, at the head of which he fought in turn the Spaniards and the English, notably at Motril, which he captured, and under the walls of Gibraltar.