Candy led his regiment under Nathaniel Banks in what became II Corps of John Pope's Army of Virginia, serving in John W. Geary's brigade of Christopher C. Augur's division. When Geary was wounded in the Battle of Cedar Mountain, Candy succeeded to brigade command. Banks's corps missed the Second Battle of Bull Run, and Candy was absent when the corps—newly dubbed XII Corps, Army of the Potomac—fought in the Battle of Antietam. XII Corps was in reserve during the Battle of Fredericksburg, but it participated in Maj. Gen. Ambrose Burnside's Mud March.