Scharner is returning to the DW Stadium having spent over five years with the Latics before leaving for West Brom in the summer of 2010.
The Austrian, who Wigan manager Roberto Martinez has brought in to play at centre-back, told the club's official website: "It really is fantastic to be back.
"Wigan will always have a big place in my heart, so to be asked to come back and help the team now is something really special for me."
The 32-year-old can also play in midfield but is currently required in defence, where Martinez is missing the likes of Ivan Ramis and Antolin Alcaraz through injury and eager to strengthen.
The Spaniard, whose side are through to the FA Cup fifth round and lie 18th in the Barclays Premier League, said: "There is no better centre-half for us to bring in than Paul Scharner.
"He knows the football club, we know him well, he has incredible experience and is a meticulous professional which means he is always in a great physical condition.
"He is desperate to come in and help the team and fight for his position. For us, it couldn't be a better option."
- Sports & Recreation
- Roberto Martinez
- Antolin Alcaraz