The short-term deal, which has yet to be confirmed by MLS or TFC, will see the 32-year-old Scot head to Canada on loan for the remainder of his contract with the Blues. Birmingham has decided not to renew its deal with Caldwell, and the English club said that the player will join Toronto immediately.
Caldwell has played for a number of clubs throughout England in his career, with notable stints at Newcastle United, Burnley, and Sunderland. He has been with Birmingham since 2011, where he featured 90 times in all competitions.
The defender has also made 12 appearances for the Scottish national side, with his most recent international match having taken place in 2011.