"We said from the beginning... that if our client remained silent we would quit his defence," he said, alongside fellow lawyer Sven Mary.
The attacks in Paris last November on bars, restaurants, a concert hall and the Stade de France killed 130 people.
So-called Islamic State said it was behind them.
Salah Abdeslam was arrested in Brussels in March and has kept silent since his transfer to France in April.
He is being monitored 24 hours a day by video in his prison cell. Mr Berton said in May the suspect was "particularly disturbed" by the surveillance.
Abdeslam is thought to have played a key role in planning the Paris attacks and transporting the attackers, but investigators are yet to determine his specific role.
The lawyers informed Abdeslam they would no longer represent him on 6 October, BFM TV reports (in French). It says that at present, he does not want to be represented by anyone else.
Legal representation is not required while the investigation continues but will be at his trial.
"The real victims of all of this are the victims of the Paris attacks, because they are entitled to this truth and they have the right to try to comprehend the incomprehensible," Sven Mary said.
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