It's understood the Belgian's new deal runs to 2015.
"I am really happy to have signed a new contract with Arsenal. I always had the intention to stay here. I feel there is a big belief in me from the club, from the boss and from the fans and that is one of the reasons why I stayed," he told arsenal.com.
"Arsenal is a fantastic club. We have great supporters, we're doing well financially and we are playing with some quality young players now and they will develop, which is very good for the future."
Manager Arsene Wenger was equally thrilled with the news, adding: "We are absolutely delighted that Thomas has signed a new long-term contract.
"Our plan is always to sign top-quality players and with Thomas extending his contract, we have done just that. Thomas is a special player, who has always made a huge contribution on the pitch and we are looking forward to him being a part of our future at Arsenal Football Club."