South Western Railway operates a train from Southampton to ExCeL London hourly. Tickets cost $28 - $45 and the journey takes 1 h 20 min. 2 other operators also service this route.
How to get from Southampton to ExCeL London
From Southampton Central train to Waterloo Underground Station, Tube to Canning Town DLR Station, train to Custom House (for ExCel) DLR Station, then walk to ExCeL London. 1 h 45 min £30. From Southampton drive to ExCeL London. 1 h 46 min £15.