The 32-year-old defender has agreed a one-year contract and will help out with the Latics' academy.
Caldwell missed large chunks of last season before coming into Uwe Rosler's plans late in the campaign, but has made over 100 appearances for the club and his manager has expressed his delight at securing the experienced defender's services for another year and helping his development as a coach.
Rosler told the official club website: "Gary has been a great servant to the club in his time here, and we are delighted we will be able to continue calling upon his experience and professionalism next season when the tension will be high and we need big characters in our dressing room.
"On the field, we saw at the end of the season what an impact he made, especially in the play-off games when he played very well - and that calmness under pressure then spreads all over the pitch.
"Off the field, we need to have a tightly-knit group to handle the intensity of the season and someone of Gary's presence is vital to build a great dressing room. He is a role model to the younger players who can see the standards he sets every day in training and on matchday.
"Whether he is playing in the team or not, he is someone who can have a major influence at the club."
Caldwell told the club's official website: "The gaffer spoke to me at the end of the season after the QPR game and said he wanted to keep me on as a player first and foremost, but also to help out with the development squad, Under-18s and the academy side of the club.
"What he described really excited me, to stay on at the club as a player but also continue coaching is a great opportunity for me.
"I want to contribute as much as I can; it's up to the gaffer how much I'll play, but for him to give me that role and responsibility with the youth team and the next generation of the club is something I'm really looking forward to."