Sanborn's brigade fought in Ulysses S. Grant's Central Mississippi Campaign from November 1862 to January 1863. That was followed by Grant's Vicksburg Campaign, with the Battle of Port Gibson on May 1, the Battle of Raymond eleven days later, and the Battle of Jackson on May 14. Sanborn also participated in the subsequent Battle of Champion's Hill, the Battle of Big Black River, and the Siege of Vicksburg from May 18 to July 4. During part of the time, he commanded a division. Sanborn's men performed garrison duty at Vicksburg following the surrender.