Eagle was appointed deputy sheriff of Prairie County, Arkansas, in 1859, a position he held until the start of the American Civil War. Eagle enlisted in the Confederate States Army and rose to the rank of colonel. He served with the 5th Arkansas Infantry and the 2nd Arkansas Mounted Rifles. He campaigned with the Army of Tennessee and fought in most of that army's campaigns from the initial battles in Kentucky all the way to the Battle of Nashville. Eagle was wounded during the Atlanta Campaign.