At the outbreak of the Mexican–American War in June 1846, Van Buren was reappointed in the army as a paymaster with the rank of major. Van Buren served as an aide to Generals Zachary Taylor and Winfield Scott and took part in the Battle of Contreras, Battle of Monterrey, Siege of Veracruz, Battle of Cerro Gordo, and Battle of Churubusco.