On October 21, he was promoted to brigadier general and placed in command of a brigade comprising the 3rd Alabama, 1st Mississippi, and 1st Virginia infantry regiments along with an artillery battery. The brigade was assigned to Maj. Gen. James Longstreet's division of the First Corps, Army of Northern Virginia. During the 1862 Peninsula Campaign, Wilcox played a prominent role at the Battle of Williamsburg on May 5.