Walker's regiment fought at the Battle of Mill Springs and Battle of Shiloh where both the unit and Walker were praised for bravery. Walker received Union general Benjamin Prentiss' sword in surrender at Shiloh. Walker was elected Colonel of the 19th Tennessee Infantry on May 8, 1862. Thereafter, he led the regiment at the Battle of Stone's River, Battle of Chickamauga and in the Chattanooga Campaign. The regiment fought during the Atlanta campaign. Fighting from trenches, they decimated the soldiers of a Union assault at the Battle of Kennesaw Mountain on June 27, 1864.