In May 1863, Breckinridge was reassigned to Joseph E. Johnston, participating in the Battle of Jackson in an unsuccessful attempt to break the siege of Vicksburg. Vicksburg fell to Grant's forces on July 4, and Breckinridge was returned to Bragg's command on August 28, 1863. After seeing no action on the first day of the Battle of Chickamauga in Georgia on September 19, he led a division of D.H. Hill's corps in an attack on the Union forces the next morning. The Confederate troops succeeded in breaking the Union line, but the main army, due at least in part to Bragg's hesitation, escaped back to Tennessee. Of Breckinridge's 3,769 men, 166 were killed in the battle; 909 were wounded and 165 were missing.