Thomas joins TFC in exchange for the club's second round pick in the 2015 MLS SuperDraft, while Caldwell extends his time with Toronto after a short loan spell from Birmingham City.
“Michael is a solid player who our coaches have had their eye on for some time,” TFC president and general manager Kevin Payne said in a club statement. “He's versatile and athletic and will be an important part of TFC for some years to come.”
Thomas, 25, began his professional career in 2010 with Swedish side Halmstads BK. After making five league appearances with Halmstads, he moved on to Ljungskile SK, where he spent more than two seasons. Thomas joined Sporting KC in 2012 and made nine appearances for the club in all competitions.
Caldwell joined TFC on May 7 and has started six matches for the Reds in central defence. His contract with Birmingham expired over the weekend, allowing the Scottish international to ink a permanent deal with Toronto.
“Steven has done a great job in anchoring our defence since arriving on loan, and he's been a terrific influence in the locker room,” Payne said. “We're very pleased that he'll be with us for this and the next two seasons.”
In Caldwell's six starts for TFC, the club has averaged one goal against per match. The 32-year-old hopes to continue helping the team in its defensive turnaround.
“I’m excited to sign for a fantastic club,” Caldwell said. “I hope to help achieve the success that I believe is coming in the not too distant future.”