During the 1863 Vicksburg Campaign, Pettus and his regiment were part of the force defending Confederate control of the Mississippi River. When the garrison surrendered on July 4, Pettus was again a prisoner until his exchange on September 12. Six days later he was promoted to the rank of brigadier general, and on November 3 he was given brigade command in the Army of Tennessee. Pettus and his brigade participated in the Chattanooga Campaign, posted on the extreme southern slope of Missionary Ridge on November 24, and fought during the action the following day.