Stewart grew up in Des Moines, Iowa, listening to his parents' jazz and rhythm and blues records without much exposure to live jazz in the then relatively isolated state of Iowa. The largely self-taught drummer began playing at the age of seven. While in high school, he played in a Top 40 cover band and the school orchestra, and went to a summer music camp at Stanford Jazz Workshop, where he met jazz legend Dizzy Gillespie. After high school graduation, Stewart attended the University of Northern Iowa in Cedar Falls, Iowa, playing in the jazz and marching bands as well as the orchestra. He then transferred to William Paterson University (then William Paterson College), where he played in ensembles directed by Rufus Reid, studied drums with Eliot Zigmund and Horacee Arnold and took composition lessons from Dave Samuels. The young drummer met future employer Joe Lovano while still in college (the two played duets in lieu of a drum lesson when Zigmund was away). Stewart also made his first recordings, with saxophonist Scott Kreitzer, and pianist Armen Donelian, while still in school, and with pianist Franck Amsallem (and Gary Peacock on bass) shortly thereafter, in 1990.