Tuchel was on the shortlist of many top clubs seeking new managers this summer, including Bayern Munich.
Neymar, 26, became the world's most expensive player last summer after Paris Saint-Germain triggered his £198m activation clause, though the capital club's talisman has been heavily linked with a move to Real Madrid in recent months.
"I can't wait to start working with all these great players who are all amongst the best in the world".
"There is extraordinary potential in Paris and this is the most exciting challenge that has come to me".
Club president Nasser al-Khelaifi was also quoted as saying on Sunday that Neymar would stay at PSG at "2,000 percent".
He is taking over from a manager who led PSG to the domestic treble in France but was nevertheless released after the big spenders failed to impress in the Champions League.
PSG's record in Europe's premier club competition does, it must be said, leave something to be desired given their vast financial resources.
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".
However, Emery - who left the Ligue 1 at the end of the season - insists that Neymar will remain in Paris. "His ambitious personality, his stated predilection for attacking football and his strength of character are all in keeping with the style that we have wanted to instil here at Paris Saint-Germain".
A falling-out with the Dortmund hierarchy cost him as job, and he had been out of work since then. The Ligue 1 title they secured with a 7-1 thrashing of their closest rival, Monaco, back in April was their fifth in seven seasons since the club was bought by Oryx Qatar Sports Investments.
Emery will take charge of his final PSG game against Caen this weekend.