Travelling by train is a great way to get from Brussels Charleroi Airport to Lille in northern France.
After your flight lands at Brussels Charleroi Airport, you can purchase a train-and-bus combination ticket at one of the two machines near Door 2 outside of the arrivals area in the airport terminal.
The ticket costs less than 15 euros and includes bus fare to the Charleroi South train station as well as train fare from Charelroi to Brussels. At that point you can change to a high-speed train to Lille, which will take you to your final destination in just 34 to 36 minutes.
After you have purchased the combination ticket, board TEC bus A from the bus stop just outside of the airport. Buses leave the airport for the Charleroi South train station every 30 minutes during weekdays and hourly during weekends.
The bus trip from the airport to the Charleroi South train station takes around 18 minutes. Once you arrive at the station, you can take a train to Brussels Midi-Zuid station, which takes around 46 to 48 minutes. When you get there, change for the train to Lille (more information on how to do this can be found here).