The Hammers needed a victory and for Tottenham to lose at home to Everton to stay up. They kept their side of the bargain, beating Leeds 3-0 at the London Stadium with second-half goals from Taty Castellanos, Jarrod Bowen and Callum Wilson.
But Spurs beat Everton to survive by two points, condemning West Ham to relegation and ending the club's 15-year stay in the Premier League.
The relegation comes a decade after West Ham's controversial move to the London Stadium and marks a rapid decline since their European Conference League triumph in 2023.
Match Summary
Leeds nearly capitalize early when James Justin's cross finds Lukas Nmecha, but the forward cannot convert. Nmecha then sets up Dominic Calvert-Lewin, only for Mads Hermansen to make a vital block.
The Hammers grow into the game, with Pablo Felipe's goalbound effort headed over by Pascal Struijk, while Karl Darlow denies Mateus Fernandes.
Two minutes before halftime, news filters through that João Palhinha has put Tottenham ahead, draining energy from the home crowd.
The breakthrough comes in the 67th minute: Bowen swings in a corner and Castellanos rises at the far post to head powerfully past Darrow.
Wilson adds the second shortly after Fernandes sends Bowen through, rounding Darlow to slot home.
Wilson completes the scoring in stoppage time, capping what is likely his farewell with a goal.
Club in Decline
The signs were there throughout the season. Supporters point to the sale of Declan Rice to Arsenal and the club's subsequent poor investment of his £105 million transfer fee.
West Ham cherry-picked budget players from relegated clubs: James Ward-Prowse, Kyle Walker-Peters and Mateus Fernandes from Southampton, Crysencio Summerville from Leeds and Mads Hermansen from Leicester.
The pattern has now come full circle. Bowen, Summerville and Fernandes are likely to be among the first out the door.
A brief revival under Nuno Espirito Santo, who replaced Graham Potter in September, began too late and fizzled out early.
Fan Anger
Fans turned their anger towards chairman David Sullivan, with chants of disappointment echoing around the former Olympic Stadium.
The 'end-of-season sale, 50% off' messages on the giant screens at the ground felt distinctly portentous as the campaign drew to a close.