The Foxes needed to win Tuesday's clash at the King Power Stadium to prolong their chance of survival, but failed to do so, briefly leading 2-1 but being pegged back.
It is the club's second relegation in as many seasons and their third in four years.
The occasion is an unwelcome full-circle moment for Leicester, who were unlikely champions of the Premier League in 2016.
They had started the season by losing just one of their first 10 games under former QPR boss Marti Cifuentes, but results started to negatively shift at the turn of the year.
Worry increased when they were deducted six points in February for breaching the EFL's spending rules, which left them one place above the drop zone.
Cifuentes was swiftly sacked and Gary Rowett took over, but results have failed to improve with just one league win he took charge.
A recent defeat to relegation rivals Portsmouth left them on the brink, with fans irate as they engaged in a spat with midfielder Harry Winks outside Fratton Park.
Fall from grace
Relegation bookends a whirlwind decade since they stunned the Premier League and all of world football.
The 5000/1 odds-defying triumph allowed them to qualify for the Champions League, and they reached the quarter-finals and finished 12th in the league the following campaign.
In 2021, they then won the FA Cup for the first time.
However, two seasons later, they were relegated despite a talented squad containing Jamie Vardy, James Maddison and Youri Tielemans.
They stormed back to the Premier League at the first time of asking as they won the Championship title under Enzo Maresca, but a campaign of difficulty would await.
Maresca left to join Chelsea before the start of last season and a combination of Steve Cooper and Ruud van Nistelrooy couldn't prevent an immediate relegation.