Manchester City will pay 100 million euros for the 18-year-old Moroccan World Cup player - equivalent to 1.1 billion kronor.
The club acted after selling Spanish midfielder Rodri to Barcelona and Tijjani Reijnders to al-Qadsiah.
Bouaddi has signed a five-year contract with Manchester City, who are also chasing Chelsea's Argentine midfielder Enzo Fernandez.
The previous highest transfer fee for a teenager was Manchester United's purchase of Leny Yoro, also from Lille, in 2024. United then paid the equivalent of SEK 760 million.
Corrected version: In a previous version, the wrong year was included for the previous record regarding a teenager.
