Stevenson commanded the 3rd Brigade, 3rd Division, XVII Corps, referred to as the "Irish Brigade" during the Vicksburg Campaign. He is most famous for making a charge at the Battle of Champion Hill which broke the Confederate left flank. On March 26, 1867, President Andrew Johnson nominated Stevenson for appointment as a brevet brigadier general in the Regular Army (United States), to rank from March 2, 1867, and the United States Senate confirmed the appointment on April 5, 1867, for his service at Champion Hill. Stevenson participated in the subsequent siege and mine explosion at Vicksburg. He later commanded the District of Corinth.