In the Gettysburg Campaign, Merritt commanded the Reserve Brigade, 1st Division, Cavalry Corps of the Army of the Potomac. He was slightly wounded in the Battle of Brandy Station; on June 29, 1863, he was appointed brigadier general of volunteers for his "gallant and meritorious service" at Brandy Station and Upperville. Being promoted directly from captain to brigadier general was an unusual step, even for the Civil War, but Merritt shared this honor on that date with Captain Elon J. Farnsworth and Captain George Armstrong Custer.