 On November 9, 1862 he was appointed brigadier general of volunteers to rank from November 29, 1862 and assumed command of the 2nd Brigade, 3rd Division, III Corps.At the Battle of Chancellorsville he commanded the 1st Brigade, 1st Division, III Corps.Upon the mortal wounding of Amiel W. Whipple, Graham assumed command of the 3rd Division, III Corps on the last day of the battle, May 4, 1863, through June 20, 1863.