The 22-year-old becomes the French champions' second acquisition of the summer window after the club triggered their option to sign compatriot Nuno Mendes permanently from Sporting Lisbon.
Vitinha is the first player to arrive at the Parc des Princes under new football advisor Luis Campos, and PSG are believed to have paid Porto a €40m (£34.5m) sum to sign the Portugal international.
Speaking to the official PSG website after completing his move on a long-term deal, Vitinha said: "I feel very, very happy. I'm honoured to be a part of this huge club.
"I feel a bit anxious but I can't wait to start working and be able to show my worth. This is what we have dreamed about since we were little kids and fortunately we are succeeding, and now that I am here I want more.
"There is no way to say no to a club like this. And when I heard of an interest, that they wanted me here, I didn't think twice and said 'yes, of course'.
"I don't like to talk about myself too much, I'd rather have other people talk about me and give their opinion. But to sum up, I'm a technical player, intelligent, who always tries to think the game through and play for the team, always doing what is best for the team.
"I like to attack, to create, I like to be the link between the back and the front. I consider myself very adult for my age. I'm cheerful too, I'm very close to my family and I get along with everybody. I don't like conflicts, what I want is the good of the team and everyone.
"Every moment is a good moment to come here. But I just had my best season without a doubt, I became an important part of the team at Porto. I won titles, it was a fantastic season. Since I'm here, I want more and I'm going to do it.
"Ligue 1 is a fast-paced league and physical too. I will try to play my game, trying to help the team all the time. I'm starting a new challenge now, a very big challenge. I'm looking forward to discovering Ligue 1."
Manchester United were also rumoured to have been interested in Vitinha before the playmaker joined PSG, and he leaves Porto after an 11-year spell with the Portuguese giants since joining their academy.
The 22-year-old scored four goals and provided six assists in 59 appearances for Sergio Conceicao's side in all tournaments, including two goals and four assists in 30 Primeira Liga matches last term.
A former Wolverhampton Wanderers loanee, Vitinha has also earned three caps for the Portugal national team and won two Primeira Liga titles, two Taca de Portugal crowns and the UEFA Youth League while at Porto.