[202] Grant ordered diversionary battles, confusing Pemberton and allowing Grant's army to move east across the Mississippi, landing troops at Bruinsburg.[203] Grant's army captured Jackson, the state capital. Advancing west, Grant defeated Pemberton's army at the Battle of Champion Hill on May 16, forcing their retreat into Vicksburg.[204] After Grant's men assaulted the entrenchments twice, suffering severe losses, they settled in for a siege lasting seven weeks. During quiet periods of the campaign, Grant would take to drinking on occasion.[205] The personal rivalry between McClernand and Grant continued until Grant removed him from command when he contravened Grant by publishing an order without permission.[206] Pemberton surrendered Vicksburg to Grant on July 4, 1863.[207]

Vicksburg's fall gave Union forces control of the Mississippi River and split the Confederacy. By that time, Grant's political sympathies fully coincided with the Radical Republicans' aggressive prosecution of the war and emancipation of the slaves.[208] The success at Vicksburg was a morale boost for the Union war effort.