Buoyed by confidence in his army after its decisive victory at Chancellorsville, Virginia, in May of 1863, Confederate Commander Robert E. Lee decided to make a second invasion in the North. Lee believed he could threaten the major cities of Harrisburg, Philadelphia, and even Washington, further eroding the dwindling support for the War in the North. Furthermore, Lee wanted to move hostilities to the North because Virginia had been ravaged by hundreds of battles. The land in the North was still unspoiled and Lee believed Confederate soldiers could subsist from the products from the pristine farms of Maryland and Pennsylvania.

On June 3, 1863, Lee directed his Army of Northern Virginia to move north from Fredericksburg. He also organized his army into three corps, Corps I led by General James Longstreet, Corps II led by Richard Ewell, and Corps III led by A.P. Hill. Cavalry would be led by J.E.B. Stuart. Confederate manpower totaled about 72,000 soldiers, whereas Union forced totaled over 94,000 soldiers.

On June 26, Major General Jubal Early's division from Ewell's Corps had reached the town of Gettysburg. Ewell's men burned railroad cars and a covered bridge, but at this point, there was no indication the largest battle in recorded history in the Western Hemisphere would occur in Gettysburg. In what would become a pivotal moment in Lee's campaign, he gave vague orders to Cavalry Commander J.E.B. Stuart to ride around the right flank of Union forces to determine exact locations and numbers. Stuart, who was indispensable to Lee in previous battles with his cavalry raids and intelligence gathering, failed to report back until the third and last day of the battle. Meanwhile, on the Union side, President Lincoln accepted the resignation of General Joseph Hooker, and replaced him with General George Meade, who would now be in charge of Union forces (the Army of the Potomac) at Gettysburg.

As Confederate forces concentrated in Cashtown, PA, about eight miles south of Gettysburg, Confederate Brigadier General Joseph Pettigrew was sent to Gettysburg to commandeer supplies, especially shoes, for the Confederate Army. Finding an enemy force at Gettysburg, Pettigrew withdrew to Cashtown, and Confederate forces began their advance.