PSG President, Nasser Al-Khelaifi, spoke of Tuchel as "one of the most competitive European coaches to have emerged at the highest level in recent years".
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Tuchel spent two years at the German giants after succeeding Liverpool manager Jurgen Klopp in 2015.
At his maiden interview, Tuchel, the former Mainz FC trainer, declared his "pride" in joining the "great world football club that is Paris St-Germain". Tuchel, though, has every confidence in his own ability, and called the challenge "by so far the most exciting proposition in football" in PSG's official communiqué.
Neymar joined PSG at the beginning of the season in a record-breaking deal from Barcelona and won a domestic treble with the club in his first season in France, scoring 28 goals in the process.
He added: "He is strongly imbued with the principles of spectacular and clinical football that have always been at the heart of German football, especially on the global scene".
Namely, Tuchel's biggest challenge, like that of his predecessors, will be finding a way to ensure PSG are ready for big Champions League matches despite facing nearly no competition domestically.
Tuchel will also have to find a way of keeping Neymar happy, providing the world's most expensive player remains in France for a second season.
A statement from PSG declared Tuchel to be "a lover of dynamic, attacking football and an accomplished tactician", and that his Dortmund side was 'always adhering to his footballing principles based on teamwork, creativity, high intensity and competitiveness'.
PSG wrapped up this season's Ligue 1 title with 5 games to spare. He can coach, but also has good man-management skills, which will be needed with the big names in the PSG squad.