I narrate a historical sociology of extension work undertaken at Queen's University, McMaster University, and the University of Toronto from the late 1800s through the early 1960s. University administrators positioned extension work as dedicated to the democratization of higher education. However, a critical analysis of archival data reveals that the rise and fall of extension reflected these universities’ material interests and organizational goals relating to public relations, government relations, and enrollment growth. Further, extension programs at these universities were primarily oriented to providing alternative credential pathways to those seeking professional status as schoolteachers, accountants, bankers, and business managers. Indeed, extension leaders demonstrated substantial agency in the professionalization of these fields. Contributing to the historical sociology of higher education and the professions, I argue that the extension era in Ontario resulted in partial democratization of higher education whilst helping to construct mechanisms of social closure rooted in credentialism and professionalization.