The clues leading to Abdeslam's arrest involved his buddy serving as a pallbearer at a suicide bomber's funeral and an unusually large order of pizza to an old lady's apartment.
Belgium is entering its third day of a security lockdown amid fears of an imminent Paris-style attack. A string of people were arrested overnight but a key suspect remains on the run.
Belgian officials have said more than one militant is feared to be at large in the city, perhaps including suspected Paris attacker Salah Abdeslam.
French authorities have released a photograph of a third unidentified suicide bomber who blew himself up outside the Stade de France.