The 22-year-old has agreed an undisclosed-length contract with the League One club.
Thomas joined the Latics on a free transfer from Charlton Athletic last season but only made three substitute appearances in the third tier and spent much of the season on loan at Sutton United.
"He brings real strength to the group, making it three centre-backs. There'll be a real fight on to get the shirt," Wimbledon first-team coach Simon Bassey told the official club site.
"Terell thought his game time at Wigan this season would probably not be as great as he would have liked.
"He's had a taste of playing first-team through his loan spells at Woking and Sutton. He has a real thirst to play games and we hope to give him that stage."
Thomas was a youth player at Arsenal and came through the ranks at Charlton in 2014.