Belgian Railways (NMBS/SNCB) operates a train from Brussels Airport (BRU) to Lille every 15 minutes. Tickets cost $20 - $23 and the journey takes 21 min. 3 other operators also service this route. Alternatively, FlixBus operates a bus from Brussels Airport (BRU) to Lille 3 times a day. Tickets cost $7 - $13 and the journey takes 2 h 15 min. Ouibus also services this route 3 times a day.
From Bruxelles-Nat.-Aéroport train to Bruxelles-Midi Eurostar then train to Lille Europe Eurostar. 1 h 57 min £58. From Brussels, Brussels Airport bus to Lille. 2 h 15 min £5. From Bruxelles-Nat.-Aéroport train to Tournai then train to Lille Flandres. 2 h 33 min £25. From Brussels Airport (BRU) drive to Lille. 1 h 16 min £15.