After the outbreak of the Civil War in 1862, he resigned his legislative seat to enlist in the 24th Iowa Volunteer Infantry Regiment. He enlisted as a private but was elected captain of his company. He remained in the Army throughout the war, receiving minor wounds at the battles of Champion Hill (Mississippi) and Winchester (Virginia). He was promoted to major in September 1864 and lieutenant colonel in January 1865 and mustered out in August 1865.