Tomori has featured regularly under Frank Lampard this season having been away on loan with Hull City, Brighton Hove & Albion and Derby County in the past.
The 21-year-old has made 16 appearances in all competitions for the Blues during the current campaign.
Tomori will join Mason Mount, Callum Hudson-Odoi, Ruben Loftus-Cheek, Billy Gilmour and Jamie Cumming in having signed new deals under the new regime.
His performances have also seen him gain recognition at full international level, with Tomori earning his first cap for England in their 4-0 win over Kosovo.
The young defender is, however, out of his side’s must-win Champions League clash with Lille on Tuesday although his hip strain is understood not to be severe.
The contract renewal talks have been ongoing for months, with the centre-back due to earn a pay rise in line with his team-mates.
Tomori has been at Chelsea since the under-8 age group and he saw a potential loan move to Everton blocked in the summer after David Luiz was sold to Arsenal.
He has repaid the faith shown in him with some impressive displays and has built up a partnership with Kurt Zouma as the Blues contended with the absence of Toni Rudiger.
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