The Hammers went into their last match of the season against Leeds sitting 18th, two points behind Spurs.
They needed to beat Leeds and hope Spurs lost at home to Everton, with Tottenham's superior goal difference meaning a draw was likely to be enough for Spurs to stay up.
West Ham delivered on their end by registering a 3-0 win, with goals from Taty Castellanos, Jarrod Bowen and Callum Wilson, but Spurs were able to grind out a 1-0 win thanks to a scrappy but vital goal from Joao Palhinha.
Relegation ends West Ham's stay in the Premier League and sends the club into the Championship for the first time in 14 years after a difficult campaign in which they were unable to recover from their position in the bottom three before the final weekend.
West Ham's fate was ultimately decided over the course of a 38-game season rather than on the final day alone, but their last fixture left them needing results elsewhere to fall their way.
Tottenham began the day on 38 points, with West Ham on 36, while the Hammers' goal difference of minus 22 left them with little margin for error.
Nuno not enough
West Ham hired Nuno Espirito Santo in September after sacking Graham Potter as manager following a dismal start to the campaign.
Despite a minor bounce, a lack of points against direct rivals ultimately proved particularly costly, ending the campaign on 39 points - two points adrift of Spurs.
By the final weeks, survival increasingly depended on results elsewhere as much as their own.
The outcome marks a significant reversal for a club that in recent years had established itself in the Premier League's middle tier while also competing in Europe, having won the Conference League in 2023.
Relegation now raises immediate questions around recruitment, player retention and financial planning ahead of life outside the top flight.
For Tottenham, who were staring down the barrel of a first top-flight relegation for 40 years, today's results provides relief but is unlikely to alter the wider assessment of their season.
However, fans will at least now be looking ahead to the future under new boss Roberto De Zerbi and will no doubt be keen to put what has been a chaotic, injury-ravaged season firmly in the back of their minds.
West Ham's attention now turns to the Championship and the scale of the rebuild required to return to the top table immediately.
West Ham will join Burnley and Wolves in the Championship next season.