The Mets recalled Thornton from Triple-A Syracuse ahead of his start against the Red Sox on Sunday.
The left-hander went back to Syracuse after delivering a quality start against the Phillies on June 26, and he'll rejoin the Mets to start the final game before the All-Star break. In addition to that outing, Thornton made one previous start in the majors this season, giving up four runs across 4.1 innings at Washington on May 20.