After his five years in service ended in 2013, Harris started his professional baseball career in the Cardinals' minor league system, making his debut with the State College Spikes of the New York–Penn League. After his absence from competition, Harris' fastball velocity had dipped to the low 80s miles per hour. However, the velocity eventually returned to the level of his college playing time. He played for State College exclusively in 2013, appearing in 20 games and going 4–1 with a 0.81 ERA and 29 SO in IP.
