Wadsworth and his division's first test in combat was at the Battle of Chancellorsville in May 1863. He made a faltering start in maneuvering his men across the Rappahannock River below Fredericksburg and they ended up being only lightly engaged during the battle. His performance at the Battle of Gettysburg was much more substantial. Arriving in the vanguard of Maj. Gen. John F. Reynolds's I Corps on July 1, 1863, Wadsworth's division bore much of the brunt of the overwhelming Confederate attack that morning and afternoon. They were able to hold out against attacks from both the west and north, providing the time to bring up sufficient forces to hold the high ground south of town and eventually win the battle. But by the time the division retreated back through town to Cemetery Hill that evening, it had suffered over 50% casualties. Despite these losses, on the second day of battle, Wadsworth's division was assigned to the defense of part of Culp's Hill. When most of XII Corps was ordered to the left flank of the army, Wadsworth sent three regiments to reinforce the brigade of Brig. Gen. George S. Greene, which was holding the summit of the hill.