The Brazilian was set to leave his role as the French champions' sporting director at the end of August but stands aside immediately following the signing of Edinson Cavani
The former Inter and AC Milan coach first moved to the French capital two years ago and has been key in PSG's building of a Ligue-winning team, helping them to bring the likes of Thiago Silva and Zlatan Ibrahimovic to the club.
However, after he received a lengthy ban for a bust-up with a referee at the tail-end of last season, he announced that he would leave the role at the end of the summer transfer window but has decided to leave the club early following the signing of Edinson Cavani from Napoli in an estimated €63 million (£54.8m) deal.
"Today was Leonardo's last day," club president Nasser Al-Khelaifi told reporters at the press conference to unveil the striker.
"I thank him for his work. He was a friend and I wish him all the best for the future. The punishment was too hard for him.
"People can leave, it doesn't change the project. I'm disappointed but I respect his decision."