Some doubt exists as to the events of the famous cavalry charge at the Battle of Somosierra, but Montbrun's share in it was most conspicuous. Soon afterwards he was promoted to General of division, and in 1809 his light cavalry division took no inconsiderable part in the victories of Eckmühl and Raab. He was employed in the Peninsular War, during 1810–1811. At the battles of Bussaco and Fuentes de Onoro, he commanded Marshal Andre Masséna's cavalry reserve.