During Sheridan’s campaign to clear the Shenandoah Valley, Washburn commanded the 4th Brigade during heavy fighting at the battles of Opequon, Fisher’s Hill and Cedar Creek. On December 12, 1864, President Abraham Lincoln nominated Washburn for appointment to the grade of brevet brigadier general of volunteers, to rank from December 15, 1864, and the United States Senate confirmed the appointment on February 14, 1865. In the winter of 1864-5, the Nineteenth Corps garrisoned the Savannah area while engaged in raids into Rebel held areas. He mustered out August 26, 1865. On May 4, 1866, President Andrew Johnson nominated Washburn for appointment to the grade of brevet major general of volunteers, to rank from March 13, 1865, for gallant and meritorious service during the war and the United States Senate confirmed the appointment on May 18, 1866.