He was promoted to brigadier general on June 3, 1862, and initially given command of three regiments from Tennessee, after the brigade commander, Robert H. Hatton, had been killed at Seven Pines. Later in June, Archer's brigade joined five others to form the "Light Division" under Maj. Gen. A.P. Hill. Soon, two more regiments were added to Archer's brigade, which fought well in the Seven Days Battles, at Cedar Mountain, and at Second Bull Run, where his horse was killed under him. His men dubbed him "The Little Gamecock" for his slight build and fierce attitude in combat.