Manchester City will pay 100 million euros for the 18-year-old Moroccan World Cup player - equivalent to 1.1 billion kronor.
The big 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 2004. United then paid the equivalent of 760 million kronor.
