Bayard fought under John C. Frémont at the Battle of Port Republic. In August 1862, at the Battle of Cedar Mountain, he led a Union Army advance. After the battle, Bayard and Confederate General J.E.B. Stuart met under a flag of truce to arrange the recovery of the dead from the battlefield. Bayard and Stuart were friends from the pre-war regular army. Stuart had been two years ahead of Bayard at West Point, and they served together in Company G, 1st U.S. Cavalry Regiment.