The 18-year-old, who was left out of Villa's pre-season tour to Australia has been linked with a move away from club all summer.
Earlier this week Villa announced they had reached an agreement with the London club - and the England youngster has now penned a six year deal at Stamford Bridge.
The midfielder, who has played 14 appearances Villa only made his debut for the club last year. However a number of eye catching performances for England Under 19s has seen his stock rise - with a number of Europe's top clubs reportedly showing interested.
Now the deal has been completed and the 18-year-old has his eyes on trophies at the London club.
He said: "It’s been quite hectic but I couldn’t get Chelsea out of my head the last few days so I’m just happy and relieved that it’s all done.
"I’m so excited and just can’t wait to get on the pitch, meet all the players and try to win games and trophies with Chelsea."
The youngster has had a busy few months - after scoring in the Under 19 European Championship Final to help England to victory - before being named in the team of the tournament.
Chelsea chairman Todd Boehly added: "Carney is one of the most exciting young players in Europe so we are really looking forward to seeing him in action at Stamford Bridge. We are delighted to be able to bring him to Chelsea and add such a talented young individual to our squad for the new season and beyond."