The regiment was assigned to Brigadier General Martin E. Green's brigade of Major General John S. Bowen's Division, of Lieutenant General John C. Pemberton's Army of Mississippi for the Vicksburg Campaign. When General Green was killed on June 27, 1863, Colonel Dockery was placed in command of Second Brigade, Bowen's Division, and so actual field command of the 19th Arkansas Regiment devolved upon Lieutenant-Colonel Dismukes, who led the regiment through the terrible battles that preceded the Siege of Vicksburg. The 19th Arkansas fought at Battle of Port Gibson, Battle of Champion's Hill, and the Battle of Big Black River Bridge, where Lieutenant-Colonel Dismukes was mortally wounded and most of the regiment was captured. Major Horatio Gates Perry Williamson was promoted to lieutenant-colonel after Dismukes' death, and the uncaptured remnant of the 19th Arkansas fell back to Vicksburg, where it endured the forty-day siege.