Mukiele, who joined Leipzig in 2018 from PSG's Ligue 1 rivals Montpellier, said farewell to the German side and their supporters on Tuesday in a social media post.
No financial details were given but media reported he had signed for 16 million euros including add ons.
"At 24, the native of Montreuil is thus returning to France by committing until 2027 to Paris St Germain, finding a region he knows by heart and a club he has met several times," PSG said on their website.
Mukiele made 146 appearances for Leipzig in all competitions and helped them reach the 2020 Champions League semi-finals and win the German Cup this year, the club's first major trophy.
PSG start their league campaign on August 6 at Clermont Foot, who have been promoted to the top flight for the first time.
