Leicester put together one of the all-time underdog sports stories when they lifted the Premier League title in 2016 but now face life in the Championship despite a 2-1 victory on Sunday over West Ham United.
Leeds will join them in England's second tier after suffering a 4-1 defeat to Tottenham Hotspur. The club led a difficult season that saw them sack managers Jesse Marsch and Javi Gracia before hiring Sam Allardyce with four games remaining.
Meanwhile, a superb strike from Abdoulaye Doucoure helped Everton to a 1-0 win over Bournemouth, maintaining the club's record of never having been relegated from the Premier League as they enter their final season at longtime home Goodison Park.
"There will be a review from people who have been here all season and will understand it," Leicester manager Dean Smith said.
"Mine was a remit to come in for seven weeks and eight games and try to keep the club in the Premier League. Unfortunately, I've fallen a little bit short."
Since winning the Premier League, Leicester had enjoyed two fifth-place finishes and won the FA Cup in 2021. However, a summer transfer window in which the club signed just one outfield player, followed by failing to win any of their opening six league games meant the club faced a fight to stay up this season.
Manager Brendan Rodgers looked to have steadied the ship soon after, with the club in 13th place when the Premier League paused for the 2022 World Cup. But a run of five losses in six matches led to Rodgers' dismissal on April 2 and the appointment of Dean Smith on an interim basis.
Leicester entered Sunday two points behind Everton, needing Sean Dyche's side to drop points, and things looked to be heading in the right direction for Smith with goals from Harvey Barnes and Wout Faes enough to secure three points.
However, Dourcoure's thunderous strike from the edge of the box on 57 minutes proved crucial and meant Everton stayed up on 36 points, two ahead of Leicester.
"Horrible day for all concerned apart from getting the job done," Dyche said. "This was the main job. We had to get it sorted out and over the line. That was the key focus. Now we must refocus on the rest of it."
Leeds, who finished five points from safety, were on the losing end of a superb display from Harry Kane, who netted twice in a convincing Spurs win.
"Most of it comes down to how good are your players?" Allardyce said. "These players have tried very hard and I can't fault their effort but as a squad they haven't been good enough by the fact that they're in the bottom three in the Premier League.
"I would have loved it if I could have got a little bit more out of them, so I take responsibility for that."
Southampton are the third side losing their Premier League status, having finished bottom of the table.