The Blues have been in advanced negotiations over a new deal for Colwill amid interest from Brighton & Hove Albion, where he spent last season on loan.
The 20-year-old has penned a heartfelt farewell to the Seagulls on social media, expressing his gratitude to the fans and manager Roberto De Zerbi.
Fabrizio Romano claims the English youngster has signed his new contract with the Blues – extending his stay at Stamford Bridge until 2029.
The official announcement from Chelsea is imminent.
Colwill enjoyed his breakout campaign in the Premier League last season, making 22 appearances in all competitions to help Brighton finish in the European places.
He received further recognition after playing a key role in England’s triumph in the recent U21 European Championship.
Colwill’s performances got the attention of his parent club Chelsea, who will integrate him into their first-team plans this season.
Chelsea manager Mauricio Pochettino has described Colwill as a fantastic talent who will have significant game time next term.
The Blues have also reached an agreement to sign Monaco defender Axel Disasi, meaning they will have a stacked defence heading into the new season.
Chelsea have been highly proactive in the transfer window, selling and signing players in equal measures as part of a squad overhaul.
They are steadfast in landing Brighton midfielder Moises Caicedo despite having a bid worth £80 million turned down by the Seagulls.
