William had a home in Memphis. He joined the Confederate Army on Jun 14, 1861 as a private along with brothers Nathan and Jeffrey. All were to receive considerably more rank as the war progressed.

July 10, 1862

Col. Nathan Bedford Forrest's brigade passed here enroute to its junction with additional units, to be followed by a further advance on the Federal garrison and stores at Murfreesboro. Leaving Chattanooga on July 9, the brigade here consisted of the 8th Texas Cavalry (Wharton), 2nd Georgia Cavalry (Lawton), and Woodward's Kentucky Cavalry Battalion, with a headquarters unit of 20 men, commanded by Captain William H. Forrest. Further accessions to strength were to join at McMinnville.

William served as a cavalry officer and led the charge against Col. Abel D. Streight's column at the Battle of Sand Mountain in Days Gap, Alabama where he was wounded April 30, 1863. William skirmished for two miles before he received a ball through his thigh, breaking the bone. Several of his men were lost in this battle. Col. Streight's men rode mules from their departure from steamships at Eastport, Mississippi. Gen. Nathan B. Forrest captured Streight's entire command on May 3, 1864 at Cedar Bluff, Alabama near the Georgia state line.

William was involved in a shooting in New Orleans, Louisiana on May 22nd, 1873. At around midnight, at the corner of Gravier and Cardondelet streets, a shot was heard. A reporter reaching the scene found that William H. Forrest had shot Joseph H. Murphy in the forehead, over his left eye. Luckily, Mr. Murphy survived. Both parties were arrested, and bonded out of jail.

March 25th, 1875-------------
"Capt. Bill Forrest, brother of Gen. N. B. Forrest, died in Memphis, Tenn., a few days ago. The deceased was a noted desperado, having killed at least five or six men in frays. A few years ago, in Marion, Alabama, he killed Col. Smith, who we believe, was his last victim. But, Capt. Forrest was a brave man, and never took undue advantage of any enemy. However - he was so dangerous that society will be better off because off his death."

William Forrest died at his brothers (Jesse A. Forrest) house at the corner of Marshall Avenue and Union Street at 8pm, on March 16th, 1875. (Contrary to the date on his grave marker.)

It was said that the only man that N.B. Forrest was scared of was his brother William Hezikiah Forrest.