At the beginning of the Civil War, he enlisted in the 4th Ohio Infantry on April 17, 1861, and was soon made a captain. He took part in the operations at Rich Mountain in western Virginia and then was promoted to the rank of major in October 1861. He served under Maj. Gen. John C. Frémont in the Shenandoah Valley, and became a lieutenant colonel in April and colonel of the 82nd Ohio Infantry in August 1862. He was engaged at the Cedar Mountain, the Second Battle of Bull Run, and Chancellorsville in XI Corps.