The corps, then led by Robert C. Schenck, played a major role in the early stages of the Gettysburg Campaign, where elements of the corps unsuccessfully opposed Robert E. Lee's initial advance through the Shenandoah.

The second division, under Robert H. Milroy, suffered heavy casualties during the Second Battle of Winchester on June 13–15, 1863, and elements of the corps also took part in the delaying action at Martinsburg a few days later.

The badly battered corps withdrew to Harpers Ferry after that, playing no further role in the campaign, until it helped join in George G. Meade's pursuit of Lee following the Battle of Gettysburg.

The VIII Corps played a major part in the defense of Washington from Jubal Early at Monocacy on July 9, 1864 under the commander of Maj. Gen. Lew Wallace.

The result was references to the Army of West Virginia as the VIII Corps even though they were never officially synonymous.