Corbet escaped in 1803 and returned to France. He was appointed professor of English at the military college of St Cyr. Later that year he became a Captain in the Irish Legion. Following the death of his brother Thomas (who was also in the Legion) in a duel with another officer, he was transferred to the 70th Regiment of the line, where he served in Massena's expedition to Portugal, and distinguished himself in the retreat from Torres Vedras and the battle of Sabugal. After the battle of Salamanca he was appointed chef de bataillon of the 47th regiment and served until 1813 when he was summoned to Germany to join the staff of Marshal Marmont. He served at the battles of Lutzen, Bautzen, Dresden and others and was made a commander of the Legion of Honour. In December 1814, he was naturalised as a French citizen. In 1815, after the abdication of Napoleon he was promoted to colonel and chief of staff to General d'Aumont at Caen.