While his brother recuperated, James Mitchell and their regiment continued to engage with the enemy, including during the battles of North Anna (May 23–26) and Cold Harbor (May 31–June 12). Assigned with his brother and their regiment to duties related to the Siege of Petersburg beginning June 9, James Mitchell then permanently became the only one of the two Mitchell brothers still fighting with the 105th Pennsylvania when his brother was honorably discharged on a surgeon's certificate of disability after having been wounded in action again on June 16, 1864.