The Morocco international, 24, was on a season-long loan to Fulham but had not scored in 12 Premier League outings this campaign.
A statement from AC Milan read: "AC Milan announces that Adel Taarabt has joined on loan from QPR, with an option to sign the player at the end of the season."
He will be hoping to change that barren run during his stay in Serie A and said: "I'm very happy to be here and it's an honour to play for the strongest team in Italy.
"I already spoke to Seedorf and he told me what he expects of me. I can't wait to start playing.
"My role? I like to play behind the forwards or even on the left or the right.
"Balotelli? I don't know him personally but it's a great honour for me to be able to play with him. I'm a player that likes to attack, score and dribble."