Initially, Davidson served in the defenses at Washington, participating in the Battle of First Manassas before he was appointed brigadier general in February 1862. He served as a division commander in the Peninsula campaign before he was assigned to the district of St. Louis. In 1863 he served as the commander of the Army of Southeast Missouri. In 1864 he commanded the Army of Arkansas. His last assignment before the end of the war was chief of cavalry of the Department of West Mississippi.
