He was the son of Joseph-Marie Sébastiani, a wealthy tailor and craftsman, and of the signora Maria Pietra Francesca Alterice Franceschi.

[2] 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)[4] 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.

He participated in the campaign of Russia, showed bravery there at the battle of Borodino, and was part of the vanguard that entered Moscow, as squadron commander of the 11th regiment of Horse Chasseurs.

At the head of the 1st brigade of the expeditionary forces, he liberated the city of Coron (on 7 October 1828)[5] from the Turkish-Egyptian occupation troops of Ibrahim Pasha.

[3] Raised to the Peerage on 3 October 1837, he followed the same line of conduct at the Luxembourg Palace (seat of the Chamber of Peers), became commander of the military division of Marseille, and, in 1842, of that of Paris, which he kept until the eve of the French Revolution of 1848.