Stevens joined the Bulldogs as a graduate transfer this offseason, reuniting with coach Joe Moorhead who was his offensive coordinator at Penn State in 2016-17.
Stevens beat out Keytaon Thompson for the starting job.
Thompson was the primary back-up to Nick Fitzgerald last season, throwing for 458 yards and six touchdowns. He also rushed for 226 yards and four scores.
The 6-foot-5 Stevens backed up Trace McSorley at Penn State last season, appearing in seven games.
"I think Tommy is a kid with a lot of physical tools. Strong arm. He can really run," Moorhead said at SEC media days last month. "He's accustomed to the system so he's going to understand it for the most part coming in. And, you know, I think he brings a lot of talent to the position, and I think the competition is going to be an exciting one."
Mississippi State opens the season at home against Louisiana on Aug. 31.