The Minister of War did not recognize Lespinasse's rank and refused to employ him for a time. Ultimately he transferred to the "Army of Italy". Soon after arriving in Italy, he forced the surrender of the Milan citadel within 11 days. Lespinasse became the army's artillery chief with Géraud Duroc serving as his aide-de-camp. On 8 June, he, Jean-Mathieu-Philibert Sérurier and François, marquis de Chasseloup-Laubat reconnoitered the fortress of Mantua. He fought at the Battles of Castiglione, Rovereto and Arcole and at the Siege of Mantua. He was several times mentioned in Napoleon Bonaparte's bulletins as being "covered in glory". Lespinasse went on Louis-Alexandre Berthier's expedition to Rome after the murder of Mathurin-Léonard Duphot. This was in January 1798. That year he was appointed chief of artillery of the "Army of England". At a later date, he and Gabriel Marie Joseph, comte d'Hédouville conducted negotiations with the rebels in Brittany.