He was promoted to brigadier general of volunteers as of September 28, 1861, and was assigned to the Army of the Potomac, where he commanded a brigade of the II Corps in the Peninsula Campaign. He was engaged at the battles of Yorktown, Seven Pines, Oak Grove, Gaines' Mill, Garnett's &amp; Golding's Farm, Savage's Station, Glendale, and Malvern Hill. French received praise in official reports for his actions and leadership, and was promoted to command a division during the Northern Virginia Campaign.