The Stonewall Brigade of the Confederate Army during the American Civil War, was a famous combat unit in United States military history. It was trained and first led by General Thomas J. "Stonewall" Jackson, a professor from Virginia Military Institute (VMI). His severe training program and ascetic standards of military discipline turned enthusiastic but raw recruits into an effective military organization, which distinguished itself from the First Battle of Bull Run (First Manassas) in 1861 to Spotsylvania Court House in 1864. Its legacy lives on in the 116th Infantry Brigade, which bears the unofficial nickname "Stonewall Brigade," and in several living history reenactment groups.

The brigade was formed by Jackson at Harpers Ferry, April 27, 1861, from the 2nd, 4th, 5th, 27th, and 33rd Virginia Infantry regiments and the Rockbridge Artillery Battery of Rockbridge County, 1 unit recruited in or near the Shenandoah Valley of Virginia. Thirteen companies of the brigade were recruited from western counties that would become part of West Virginia. It was officially assigned to the Virginia Provisional Army, then to the Army of the Shenandoah on May 15, and the Valley District on July 20.

The Stonewall Brigade was initially armed with weapons captured from the arsenal at Harpers Ferry; its regiments went to First Bull Run carrying a wide range of muskets from Model 1816/1822 muskets converted to percussion to modern Model 1855 rifles to VMI cadet muskets (a Model 1842 musket downsized to .58 caliber). Company K of the 33rd Virginia, the Shenandoah Sharpshooters, had the misfortune of getting flintlock muskets. In September, Jackson received a request from Virginia governor John Letcher asking for the return of the VMI muskets (carried primarily by Company H of the 4th Virginia, known as the "Rockbridge Grays"). Jackson replied back that the muskets could not be returned until better weapons became available.

Jackson's brigade was referred to informally as "Virginia's First Brigade" until July 21, 1861, when, at First Manassas, both the brigade and its general received the nickname "Stonewall". General Barnard E. Bee of South Carolina is said to have made his immortal remark as he rallied his brigade for the final phase of the battle. Although the exact words were not recorded at the time, he probably said, "There stands Jackson like a stone wall. Rally behind the Virginians!" This is considered the turning point of the first major battle of the American Civil War, and the Union troops were repulsed and sent reeling back toward Washington D.C. in defeat. Jackson was promoted to higher command, but the brigade remained under his overall command until his death. Upon Jackson's promotion, he was replaced as brigade commander by Brig. Gen. Richard B. Garnett that fall.

In the fall of 1861, Jackson was promoted to division command and reassigned to the Shenandoah Valley and Potomac River area, where they overwintered. During this time, a trickle of better weapons reached the Stonewall Brigade as Confederate agents began purchasing rifles from Europe. However, the brigade still had a large number of smoothbore muskets until the Gettysburg Campaign, by which time the majority of its men had .58 caliber rifles.

On March 13, 1862, the Valley District was incorporated into the Army of Northern Virginia, under General Joseph E. Johnston. Jackson and the Stonewall Brigade operated in the Valley as part of the left wing of Johnston's army. During Jackson's Valley Campaign, Jackson's only defeat of the Civil War occurred at the First Battle of Kernstown on March 25, 1862. After receiving faulty intelligence, the brigade was ordered to attack a much larger Union force. Out of ammunition and almost surrounded by the superior force, Garnett ordered a withdrawal. Jackson was infuriated by this action, taken without his explicit permission, and Garnett was relieved of command and subject to court martial (Garnett was later killed during Pickett's Charge in the Battle of Gettysburg, attempting to restore his military honor).

For the remainder of the Valley Campaign, Brig. Gen. Charles S. Winder commanded the brigade and there were no more defeats in store. The brigade marched over 400 miles in four weeks, was victorious in six significant battles, and helped Jackson achieve a strategic victory in the Eastern Theater. The brigade's mobility in the campaign (particularly a 57-mile march in 51 hours) earned it the oxymoronic title "Jackson's foot cavalry".

At the end of the Valley Campaign, the brigade moved to reinforce General Robert E. Lee in the Seven Days Battles on the Virginia Peninsula. In the Battle of Gaines' Mill, the brigade assaulted the Federal right and helped Lee achieve a victory. In the Northern Virginia Campaign, the brigade suffered high casualties at the Battle of Cedar Mountain and General Winder was killed on August 9, 1862. Jackson personally rallied his old brigade and won the battle. The brigade would suffer more casualties in the Second Battle of Bull Run. On August 30, 1862, the Stonewall Brigade repulsed the attack of the Union's Iron Brigade and rallied for a counterattack. Its acting commander, Colonel William S. Baylor, was killed. Colonel Andrew J. Grigsby assumed command and led the brigade through the Maryland Campaign and the Battle of Antietam. The brigade defended the West Woods, where the fighting was so severe and attrition so high that Grigsby was commanding the division ("Jackson's Division") by the end of the day.