Cassagne led his regiment at Auerstadt and Pułtusk in 1806 and Eylau in 1807. He was promoted general of brigade in 1807 and became Baron of the Empire in 1808. He transferred to Spain and was captured at Bailén. After exchange he served at Talavera and Cadiz. Promoted to general of division in 1813, he led a division that year at Vitoria. Transferring to Germany he led a division at Dresden and was captured when that fortress surrendered. During the Hundred Days he was employed by Napoleon on the Spanish frontier. Placed on inactive duty during the Bourbon Restoration he was recalled to active duty in 1833 and retired six years later. His surname is one of the names inscribed under the Arc de Triomphe, on Column 27.