Chelsea yesterday paid Porto £13.3m to activate his release clause so Villas-Boas could join the Blues and having agreed personal terms today he has been unveiled as their new chief.
Villas-Boas was previously at Chelsea under Jose Mourinho he is already familiar with the club.
Chelsea released a statement on their website and it said; "Chelsea Football Club is delighted to announce that Andre Villas-Boas will be the club's new manager.
"He has signed a three-year contract and will start work immediately.
"Andre was the outstanding candidate for the job. He is one of the most talented young managers in football today and has already achieved much in a relatively short space of time.
"His ambition, drive and determination matches that of Chelsea and we are confident Andre's leadership of the team will result in greater successes in major domestic and European competitions.
"Andre will bring his coaching experience back to a club he is already very familiar with, having previously worked here for three years.
"He has always been highly regarded at Chelsea and everyone here looks forward to welcoming him back and working with him."
