A childhood friend of suspected ringleader Abdelhamid Abaaoud, Abdeslam is thought to have played a key role both on the night of the Paris attacks on November 13, and in their preparation.
Two others have been arrested in France in connection with the attacks carried out by the Islamic State group, but they are considered secondary participants.
Abdeslam played a key role, dropping off the three suicide bombers who blew themselves up outside the Stade de France national stadium in northern Paris.
He is thought to have backed out of blowing himself up. Authorities found an abandoned explosives vest in a southern Paris district close to where mobile phone data placed him on the night of the attacks.
CCTV pictures from petrol stations showed him fleeing back to Belgium after two friends came to pick him up.
He also played a critical role in the build-up to the attacks, renting the cars and hideouts used by the gang.
He also transported several other jihadists around Europe in the preceding months, including Najim Laachraoui, the suspected bombmaker for the November attacks who was killed in a suicide bombing in Brussels on March 22.