West Brom have been relegated from the Premier League after Southampton's 1-0 win at Swansea City on Tuesday.
Darren Moore's men needed the game at the Liberty Stadium to end in a draw to keep their survival hopes alive, but Manolo Gabbiadini's winner confirmed West Brom's relegation.
The Baggies go down despite a 1-0 win over Tottenham on Saturday, a result that extended their unbeaten run to five games.
The club joins Stoke City, who were relegated on Saturday after they lost 2-1 to Crystal Palace , in dropping from the top flight.
West Brom will head to the Championship after an eight-year stay in the Premier League, having last played in England's second tier in the 2009-10 campaign.