While the Tullahoma Campaign unfolded King was unfit to command his men in the Battle of Hoover's Gap as his hand hadn't fully healed yet. Meanwhile, he had also been made Lieutenant Colonel of the 14th U.S. Infantry Regiment though he didn't serve in the capacity. However he returned to duty with the brigade shortly afterwards and in July briefly led the division. In September, now with Absalom Baird leading the division, King commanded his brigade in the Battle of Chickamauga; suffering the highest loss percentage of any Union brigade in those days with 56%. He would later be brevetted to Colonel for his role in that battle. He then led his men into the Chattanooga Campaign in which the brigade was augmented by the 11th Michigan Infantry, 19th Illinois Infantry and 69th Ohio Infantry regiments; where it participated in the Battle of Missionary Ridge, King missing the later due to sickness.