The 27-year-old's temporary move has been confirmed after he passed a medical and he will wear the No 29 shirt for the Latics.
Maynard has found his opportunities limited at Cardiff this season after missing most of last term due to injury following a £2.5m move from West Ham in August 2012.
The former Crewe and Bristol City player has made 10 appearances in all competitions for the Bluebirds this season with his only goal coming against Accrington in the Capital One Cup.
Wigan manager Uwe Rosler told his club's official website: "Nicky is at the stage of his career where he wants to play regular football again after his injury last season. He wants to prove a point to himself and also to the people.
"That's a perfect scenario for us; it matches our ambitions. We want to prove a point, we want to go up, we want to into the play offs and I think we can give him the platform to perform again.
"I will be patient with him because he has not played in a while. But, he's fit, and he's ready to go."
Maynard is now likely to make his Wigan debut in Saturday's Championship game at Doncaster.