In January 1861, he resigned a captaincy in the 10th United States Infantry to accept the Lieutenant Colonelcy of the Augusta Volunteer Battalion. He soon resigned that position to become major of the 1st Georgia Infantry. By June, he was the Lieutenant Colonel of the 10th Georgia Infantry Regiment and four months later its colonel, succeeding Lafayette McLaws. He served with distinction during the Peninsula Campaign of 1862, including the Battle of Yorktown, the Battle of Savage's Station, and the Battle of Malvern Hill, where he was wounded. His performance earned him the temporary command of an Alabama brigade prior to the Maryland Campaign due to the illness of Brigadier General Cadmus M. Wilcox.