Investigators nabbed Paris attacks suspect Mohamed Abrini in a police operation in the Anderlecht district of Brussels.
He has been linked to the terror attacks in Paris on November 13 through surveillance video and DNA, a CNN report said.
Officials will now question him about the Brussels airport bombing on March 22, part of the attacks that killed 34 people and injured several.
Two attackers died at the airport. A third man was seen on video walking with them. Authorities said he fled.
Investigators are trying to find hether Abrini, who was arrested in a separate operation on Friday, was part of the second attack -- at a Brussels metro station .
Osama Krayem -- also known as Naim al Hamed -- might be the second person "present at the time of the attack at the Maelbeek subway station," Belgian federal prosecutor's spokesman Eric Van der Sypt said.
Officials have said Khalid El Bakraoui carried out the metro attack and Van der Sypt said another person was seen with El Bakraoui before the subway blast.
Abrini, a 31-year-old Belgian-Moroccan, was being among Europe's most wanted and was considered "armed and dangerous".
His arrest means that Belgian authorities now have at least two people, along with Salah Abdeslam, who have been directly tied to the attacks in Paris that left more than 130 people killed.
His fingerprints and DNA were lifted from a vehicle used in the Paris attacks, an official said.
Days after Abdeslam was arrested, terrorists carried out twin attacks in Brussels. A senior official has said Abdeslam was probably going to be part of an attack planned by the same Islamic State cell.