Alfa-Ruprecht has moved to Bayer for a compensation fee of €1.3m and has signed a deal to 2030.
The Hamburg-born winger told Bayer's website: "Leverkusen is a top club with great visibility. I will repay the trust placed in me and give everything to deserve the Bayer jersey."
Sporting director Simon Rolfes said: "Farid Alfa-Ruprecht has caused a stir as a winger in the English U21 Premier League. His excellent goalscoring rate, great pace, and remarkable footballing talent make him a very interesting candidate for our first team."
Director of Football Kim Falkenberg added: “We see clear potential in Farid to become an important player for Bayer 04 in the long term.”
