"It is a good piece of news, it ends the debate on whether we will shop for another centre-back because we now have five so we will not be on the market in that area," Wenger told reporters before his side's Champions League game against Olympique Marseille at the Stade Velodrome on Wednesday.
Vermaelen, 25, has been injured since August but is now closing in on a return to full fitness said he was delighted to commit his future to the club.
"I am really happy to have signed a new contract with Arsenal. I always had the intention to stay here," he told the club's website.
"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."
It was not clear when Vermaelen's extended contract would end but media reports suggested it would be after the 2014/15 season.
Vermaelen, who has 32 caps, joined Arsenal from Ajax Amsterdam in 2009 but his spell at Emirates Stadium has been plagued by injuries.
He only made five appearances last season and has missed Arsenal's last nine matches after surgery on an injured ankle.
"Thomas is a young boy as well, people forget," Wenger was quoted as saying on the club's official website.
"If you take [Johan] Djourou, [Per] Mertesacker, [Laurent] Koscielny and Vermaelen, they are all 25 or 26-years-old so as centre-backs they have 10 years in front of them."
