"I’m looking forward to being a part of this young, dynamic squad led by Frank Lampard as we challenge for honours next season. I can’t wait to get started and hopefully it won’t be long before we’re playing in front of the Chelsea fans at Stamford Bridge."
Chilwell came through Leicester's youth academy to become a key player for the senior team, making 123 appearances and helping them to win the Premier League title in 2016.
Further additions are expected as the Stamford Bridge outfit made progress in their pursuit of Bayer Leverkusen playmaker Kai Havertz this week, having agreed to match the Bundesliga team's £90m ($118m) asking price.
Chelsea are expected to strengthen even further at the back this week, as 35-year-old Thiago Silva is close to joining following his departure from Paris Saint-Germain as his contract expired after their Champions League final defeat to Bayern Munich.
They have already waved goodbye to Pedro and Willian after their contracts expired. The Spain international completed a switch to Roma this week, while Willian joined Arsenal on a three-year deal earlier this month.