Villas-Boas, who was sacked by Chelsea in March after less than a season at Stamford Bridge, has signed a three-year contract and replaces Harry Redknapp, who was dismissed by Tottenham in June.
Villas-Boas said: "Tottenham Hotspur is a great club with a strong tradition andfantastic support, both at home and throughout the world. I feel privileged to be its coach. For me, this is one of the most exciting coaching positions in the Premier League.
"I have had several discussions with thechairman and the board and I share their vision for the future progress of the club. This is a squad any coach would love to work with and together Ibelieve we can bring success in the seasons ahead."
Spurs also considered former France coach Laurent Blanc and Schalke 04 boss Ralf Rangnick, while Everton manager David Moyes had been a serious contender before chairman Daniel Levy cooled his interest.
Villas-Boas, 34, will be charged with creating a young Spurs side that can challenge for a place in the top four of the Premier League and qualification for the Champions League.
The Portuguese was hugely successful at Porto prior to his move to Chelsea, winning the Primeira Liga, Portuguese Cup and the Europa League in his one season in charge at Estadio do Dragao.
Commenting on the new appointment, Levy told Tottenham's official website:"I am delighted that Andre has agreed to become our new head coach. He has an outstanding reputation for his technical knowledge of the game and for creating well-organised teams capable of playing football in an attractive and attacking style.
"Andre shares our long-term ambitions and ethos of developing players and nurturing young talent, and he will be able to do so now at a new world class training centre.
"We are constantly looking to move theclub forward. It is important that we now look to develop the potential within the squads at all levels, whilst strengthening the first team in the summer in key positions with players who will become part of the future success of the club."
Villas-Boas will be joined by fitness coach Jose Mario Rocha and Daniel Sousa, head of opposition scouting, at White Hart Lane.