Thornton was traded from the Astros to the Blue Jays in exchange for Aledmys Diaz on Saturday, Ben Nicholson-Smith of Sportsnet.ca reports.
Thornton has yet to make his major-league debut after spending four seasons in the minors. He posted a 4.42 ERA and 1.20 WHIP with 122 strikeouts over 124 innings with Triple-A Round Rock in 2018 and figures to have a shot to win a spot in Toronto's starting rotation next spring.