Boss Karl Robinson told the club's official website: "He is someone I tried to sign, ironically, 12 months ago this very day. He has great experience even though he's only 25.
"We're very light in the wide areas at the moment but he's going to bring tremendous quality. It's quite an exciting one for us. He's somebody who'll create a lot of goals. We feel we've got goals in the team and hopefully he can add to the assists.
"He is coming here to get games but he is also coming here to prove a point to Charlton as well. In the time that he spends here we are going to get performance levels, he's going to lift the group in the short term because he's a quality player.
"We're in a good position, we're sixth in the League and we don't want to sit on our laurels, it's my job to keep us pushing forward and we feel we can do that with the acquisition with Danny Green."