Around 7 pm (19:00), as dusk began to fall, and the Confederate assaults on the Union left and center were slowing, Ewell chose to begin his main infantry assault. He sent three brigades (4,700 men) from the division of Maj. Gen. Edward "Allegheny" Johnson across Rock Creek and up the eastern slope of Culp's Hill. The Stonewall Brigade, under Brig. Gen. James A. Walker, had been dispatched earlier in the day to screen the Confederate left flank to the east of Rock Creek. Although Johnson ordered Walker join the dusk assault, he was unable to do so as the Stonewall Brigade sparred with Union cavalry under Brig. Gen. David M. Gregg for control of Brinkerhoff's Ridge.^[93]

On the Confederate right flank, Jones's brigade of Virginians had the most difficult terrain to cross, the steepest part of Culp's Hill. As they scrambled through the woods and up the rocky slope, they were shocked at the strength of the Union breastworks on the crest. Their charges were beaten off with relative ease by the 60th New York, which suffered very few casualties. Confederate casualties were high, including General Jones, who was wounded and left the field.

In the center, Nicholls's Louisiana brigade had a similar experience to Jones's. The attackers were essentially invisible in the dark except for brief instances when they fired, but the defensive works were impressive, and the 78th and 102nd New York regiments suffered few casualties in a fight that lasted four hours.^[94]

Steuart's regiments on the left occupied the empty breastworks on the lower hill and felt their way in the darkness toward Greene's right flank. The Union defenders waited nervously, watching as the flashes of the Confederate rifles drew near. But as they approached, Greene's men delivered a withering fire.

Two regiments on Steuart's left, the 23rd and 10th Virginia, outflanked the works of the 137th New York. Like the fabled 20th Maine of Col. Joshua L. Chamberlain on Little Round Top earlier that afternoon, Col. David Ireland of the 137th New York found himself on the extreme end of the Union army, fending off a strong flanking attack. Under heavy pressure, the New Yorkers were forced back to occupy a traversing trench that Greene had engineered facing south. They essentially held their ground and protected the flank, but they lost almost a third of their men in doing so. Because of the darkness and Greene's brigade's heroic defense, Steuart's men did not realize that they had almost unlimited access to the main line of communication for the Union army, the Baltimore Pike, only 600 yards to their front. Ireland and his men prevented a huge disaster from befalling Meade's army, although they never received the publicity that their colleagues from Maine enjoyed.^[95]

During the heat of the fighting, the sound of battle reached II Corps commander Maj. Gen. Winfield Scott Hancock on Cemetery Ridge, who immediately sent additional reserve forces. The 71st Pennsylvania filed in to assist the 137th New York on Greene's right.^[96]

By the time the rest of the XII Corps returned late that night, Confederate troops had occupied some of the Union defensive line on the southeastern slope of the hill, near Spangler's Spring. This caused considerable confusion as the Union troops stumbled in the dark to find enemy soldiers in the positions they had vacated. Gen. Williams did not want to continue this confused fight, so he ordered his men to occupy the open field in front of the woods and wait for daylight. While Steuart's brigade maintained a fragile hold on the lower heights, Johnson's other two brigades were pulled off the hill, also to wait for daylight. Geary's men returned to reinforce Greene. Both sides prepared to attack at dawn.^[97]