Stewart was promoted to the major leagues Sunday, Ken Gurnick of MLB.com reports.
Stewart will take the roster spot of Yasiel Puig (ankle), who's headed to the 10-day disabled list. The 26-year-old has been impressive at Triple-A Oklahoma City through four starts, accruing a 2.41 ERA and striking out 20 across 18.2 innings. With Rich Hill (finger) unable to make Monday's start against the Giants, Stewart is a prime candidate to get the nod in what would be his first big-league outing of the season.