A self-taught man, Forrest bought and sold horses, cattle, and slaves before acquiring considerable wealth as a cotton planter in Mississippi. At the outbreak of the war, he raised a cavalry unit and, as a lieutenant colonel, took part in the defense of Ft. Donelson, Tenn. (February 1862). Refusing to capitulate with the rest of the Confederate forces, he made his way out before the fort was surrendered. After fighting with distinction at the Battle of Shiloh, Tenn. (April), he was promoted to brigadier general and took a brilliant part in the autumn campaign. The following winter he was continually active in raiding hostile lines of communication.

In keeping with Confederate policy at that time, Forrest—by then a major general—ordered his troops to “take no more Negro prisoners” when they assaulted and captured Ft. Pillow. A Congressional investigation committee verified the slaughter of more than 300 black men, women, and children within the fort.

In June 1864 Forrest decisively defeated a superior Union force at Brice's Cross Roads, Miss., and throughout the year he conducted successful raids in Mississippi, Tennessee, and Alabama. He was once more with the main Confederate Army of the West in the last disastrous campaign of Nashville (December) and fought a stubborn rearguard action to cover the retreat of the broken army. He was forced back at Selma, Ala., in April 1865 and surrendered his entire command in May.

After the war he was active in the railroad business, and was a leading organizer and the first Grand Wizard of the original Ku Klux Klan, a secret society advocating white supremacy.