Fetha Malki, a Toulouse resident with a history of petty crimes, was charged over the weekend with complicity in murder in connection with a terrorist enterprise and ordered held without bail.
He faces other charges of receiving stolen goods and selling illegal weapons.
Judicial sources said the man admitted on Saturday to having provided Merah with arms following his arrest on Tuesday but denied any advance knowledge of his attacks.
Claiming inspiration from Al-Qaeda, Merah shot dead a rabbi, three Jewish children and three French paratroopers in March last year, before being killed during a stand-off with police at his home.
Two others have been charged in the investigation, his brother Abdelkader who faces charges of complicity in murder and a man suspected of taking part in the theft of the scooter Merah rode during his attacks.
Malki is suspected of having provided at least two firearms to Merah, including an Uzi submachine gun used during his attack on a Jewish school.
He is also suspected of supplying the body armour worn by Merah during the police siege of his apartment.