The 29-year-old has been on the lookout for a new club since leaving Burnley and has now linked up with brother Gary at the DW Stadium.
Wigan have endured a difficult start to the campaign after following up their 4-0 thrashing by Blackpool with a 6-0 thumping from Chelsea.
Caldwell has been training with Wigan in recent weeks and clearly made a favourable impression on under-fire manager Roberto Martinez.
Martinez believes he has landed a leader on and off the pitch and feels his experience will prove invaluable to the cause.
"We have seen what Steven is all about during his time here," he told the club's official website. "He's a leader on and off the field and he is a great personality to have in the dressing room.
"He has shown real professionalism in his time with us and we are delighted to have him on board.
"He has good experience of the Premier League and has played in the Champions League and UEFA Cup, plus is a full Scotland international.
"He is a totally committed defender who will add fantastic competition to the squad."
Caldwell is thrilled to have linked up with his brother at Wigan and admits Gary has given positive reviews of the Lancashire side.
"Gary has of course told me what the club is like and how impressed he has been with the set-up here, and I am delighted to have sorted out my future now," said Steven. "I have already got to know the lads over the past few weeks and I can't wait to get started and fight for my place."