On October 27, the battalion, officially designated the 7th Missouri Infantry Battalion, began moving towards Fort Smith, Arkansas, where a Confederate army was being organized. The unit did not reach the camp of Brigadier General Mosby M. Parsons, to whose brigade the battalion was assigned, until November 28. One day later, three companies from Frazier's Missouri Infantry Battalion were added to the 7th Missouri Infantry Battalion; the combined unit was still considered a battalion. When Parsons moved northward in the direction of Prairie Grove on December 3, the battalion accompanied the brigade. Four days later, Parsons' brigade saw action at the Battle of Prairie Grove. Early in the fighting, Parsons' brigade was aligned in a position guarding the Confederate left, along with Brigadier General John S. Roane's brigade. The 7th Missouri Infantry Battalion, known as Mitchell's Missouri Infantry during the battle, served as Parsons' reserve.