The medical was completed late on Monday night to ensure the deal was done on deadline day, per Sky Sports.
Advertisement
Advertisement
The deal is reportedly worth £51 million as Newcastle have reached £262 million in spending this summer.
Newcastle view the signing as being on par with there acquisition of Nico Gonzalez from Manchester City this summer, as new boss Matthias Jaissle continues to rebuild his side.
The Belgian notched eight goals and registered five assists for Lille last season, as they finished third in Ligue 1.
The news comes as Nick Woltemade is set to complete a season long loan to Juventus.