At the beginning of the Civil War, he joined the 8th Missouri Volunteer Infantry, in which he became a captain. He took part in the capture of Fort Donelson, the Battle of Shiloh, and the operations against Corinth, becoming, later in 1862, colonel of a regiment which he led at Chickasaw Bayou. After the final campaign against Vicksburg, on August 4, 1863 he was appointed brigadier general of volunteers to rank from August 4, 1863. He was wounded at the Third Battle of Chattanooga. He took part in the Atlanta Campaign, the March to the Sea and the Carolinas Campaign. He was appointed to the rank of major general of volunteers on November 24, 1865, the last one based on seniority for the Civil War.