The prosecutors said they found Salah Abdeslam's fingerprint in a search of the apartment on December 10, but would not say why they waited a month to announce it.
The search also turned up three suspected suicide belts, traces of the same explosive used in the November 13 attacks that killed 130 people and other material that could be used to manufacture bombs, according to the Belgian Federal Prosecutor's Office.
"We found material to make explosives, we found traces of explosives and we found three belts. So you don't have to be Sherlock Holmes to make the right deduction," Van der Sypt told The Associated Press.
Abdeslam is believed to have played a key logistical role in the Paris attacks. A French gendarme stopped him and his two friends in their car near the border but released them. The friends are among 10 people arrested in Belgium in connection with the attacks.
The apartment in the Schaerbeek neighbourhood of Brussels had been rented under a false identity that may have been used by one of those who are now under arrest.
The prosecutor's office said the three handmade belts discovered in the search at Rue Berge in Schaerbeek "could have been intended for the transport of explosives." Traces of the highly volatile TATP, which was packed into the suicide vests in November, as well as other material that could be used to manufacture explosives were also detected.