The Netherlands under-21 international has signed a contract at the Bay Arena until the summer of 2025.
Bakker joined PSG from Ajax Amsterdam in the summer of 2019 and made 45 appearances in his time at the club.
The 21-year-old left back won one Ligue 1 title, two Coupe de France, one Coupe de la Ligue and one Trophees des champions during his spell in the French capital.
"It's a chance to take the next step in my development at an attractive club," Bakker told Leverkusen’s website on signing.
"The whole package at Leverkusen convinced me. The people in charge made a real effort with me, were very target-focused. The club is ambitious and so am I. It's a good fit."
Leverkusen sporting director Simon Rolfes added:"Mitchel Bakker is a technically skilled and dynamic full-back, whose profile fits perfectly with Bayer 04."
"He is still young and capable of development, but has already gained experience at the very highest level with a top European club.
"Mitchel was an important player for PSG, especially under coach Thomas Tuchel, and he will lift the quality of our squad. We are sure he is in for a successful future."
Leverkusen finished sixth in Bundesliga last season and will begin the 2021/2022 campaign away at Union Berlin on August 14.
