Stewart enrolled at Princeton in 1928 as a member of the class of 1932, majoring in architecture and becoming a member of the Princeton Charter Club. He excelled academically, but also became attracted to the school's drama and music clubs, including the Princeton Triangle Club. Upon his graduation in 1932, he was awarded a scholarship for graduate studies in architecture for his thesis on an airport design, but chose instead to join University Players, an intercollegiate summer stock company performing in West Falmouth, Massachusetts, on Cape Cod.