The 32-year-old's arrival at Highbury ends Gunners manager Arsene Wenger's protracted search for goalkeeping reinforcements following an injury to Rami Shaaban.
Wenger wanted back-up to David Seaman and Stuart Taylor and has landed the former Lens shot-stopper before the close of the transfer window.
"Since the injury to Rami Shaaban, it was very important that we brought in another goalkeeper as cover," Wenger told the club's official website.
"Of course, we are very pleased to have signed Guillaume. He is a very experienced player and has proved during his time with Lens that he is a very capable goalkeeper."
Though Warmuz will be ineligible for the Champions League, having played in the competition for Lens this term, he was overjoyed at clinching a short-term deal in North London.
Warmuz said: "I am delighted to be joining Arsenal. They are a team full of world class players and I am looking forward to playing for one of the best clubs in Europe."
