Throughout the evening of July 1 and morning of July 2, most of the remaining infantry of both armies arrived on the field, including the Union II, III, V, VI, and XII Corps. Two of Longstreet's divisions were on the road: Brigadier General George Pickett, had begun the 22-mile (35 km) march from Chambersburg, while Brigadier General Evander M. Law had begun the march from Guilford. Both arrived late in the morning.

The Union line ran from Culp's Hill southeast of the town, northwest to Cemetery Hill just south of town, then south for nearly two miles (3 km) along Cemetery Ridge, terminating just north of Little Round Top.^[58] Most of the XII Corps was on Culp's Hill; the remnants of I and XI Corps defended Cemetery Hill; II Corps covered most of the northern half of Cemetery Ridge; and III Corps was ordered to take up a position to its flank. The shape of the Union line is popularly described as a "fishhook" formation.^[59]

The Confederate line paralleled the Union line about one mile (1,600 m) to the west on Seminary Ridge, ran east through the town, then curved southeast to a point opposite Culp's Hill. Thus, the Union army had interior lines, while the Confederate line was nearly five miles (8 km) long.^[60]

Lee orders two of his generals, James Longstreet and Ewell, to attack the flanks of Union forces on Culp's Hill. But Longstreet delays, and attacks much later than Ewell, giving Union forces more time to strengthen their position.

The Union's Maj. Gen. Daniel Sickles advances in front of the main line and comes under attack. The two sides engage in some of the fiercest fighting of the Civil War, ensuring that the locations Peach Orchard, Devil's Den, the Wheatfield and Little Round Top go down in history. Ewell attacks Union troops at Cemetery Hill and Culp's Hill, but Union forces hold their position.