Leslie Workman is widely recognized as the founder of the academic subject known as Medievalism: the study of the Middle Ages as an imaginative construct in western society since whenever the Middle Ages may be said to have ended. He himself defined the subject as "the continuing process of creating the Middle Ages." In 1971 he initialed the formal scholarly investigation of medievalism through sessions at the International Congress on Medieval Studies at Western Michigan University.

In 1976 he founded the scholarly journal Studies in Medievalism, serving as its editor until 1999. In 1986 he established the International Conference on Medievalism, an annual meeting of scholars which has convened throughout the United States and in England and Austria. He was also the organizer of the four-week Summer Institute on Medievalism at the University of York in 1996 and 1998. In 1998 his achievement received formal recognition by the publication of Medievalism in the Modern World: Essays in Honour of Leslie Workman.