In September 1863, the Union army in Tennessee was defeated at the Battle of Chickamauga and two corps were sent west to help them as they were besieged in Chattanooga—the XI and XII Corps. (They later were combined due to their small sizes into a new XX Corps, Army of the Cumberland.) Williams' division did not reach Chattanooga, but guarded railroads in eastern Tennessee. However, it did join Maj. Gen. William T. Sherman as part of XX Corps in the Atlanta Campaign and fought with distinction in a number of battles, particularly the Battle of Resaca. Williams was wounded in the arm at the Battle of New Hope Church on May 26, 1864. His division followed Sherman through his March to the Sea and the Carolinas Campaign. In these campaigns Williams lead XX Corps until, following the Battle of Bentonville, Joseph A. Mower was given command. Williams resumed leading his division. During this period, Williams received a brevet promotion to major general on January 12, 1865.