Stewart was recalled from Triple-A Oklahoma City on Tuesday.
He takes the place of Luis Avilan, who was placed on the paternity list as a corresponding move. While Stewart is an option to start when a need arises, he will likely head to the bullpen and serve as a multi-inning reliever, while staying on something resembling a starter's schedule. Stewart did not allow a run while striking out 10 in 13 innings as a reliever earlier this year.