Tuchel, 44, who had been out of work since leaving Borussia Dortmund in May 2017, signs a two-year contract with the mega-rich Paris-based club.
"There is extraordinary potential in Paris and this is the most exciting challenge that I have received".
"Thomas is one of the best and most competitive European coaches to have emerged over the last few seasons", declared PSG president Nasser Al-Khelaifi. "He has the mix of spectacular and effective principles that have always been the true strength of German football".
Both Marcelo and Neymar were named in Brazilian manager Tite's 23-man squad for the World Cup this summer, but the left-back has revealed that talk in Russian Federation will be exclusively fixed on the tournament and not on club football.
The German will be tasked with delivering success to PSG on the European stage, with the club failing to deliver in the Champions League since Qatar Sports Investments took ownership of the French giants in 2011.
A strong disciplinarian, he could end up being an excellent choice for PSG, a club where star players have often enjoyed too many privileges in the past.
However, Tuchel - a modest player whose career was cut short by a knee injury - is not yet proven as a coach at the highest level.
PSG wrapped up this season's Ligue 1 title with 5 games to spare.
This is a unique problem (even Bayern Munich, who are the closest comparison to PSG in terms of domestic dominance, face stiffer competition in the Bundesliga, and their Champions League record perhaps suggests they suffer from the same lack of weekly competition anyway), and its solution is unlikely to be primarily tactical.
The Brazilian had two reasons to celebrate on Saturday as he also turned 30, but his attention will be quickly drawn to Real's final La Liga match of the season this weekend as the club take on Villarreal at the Estadio de la Ceramica.