Born in Rice Lake WI in 1950, Leary grew up fascinated by the dialects, stories, music, and customs of his culturally diverse neighbors, and through part-time work on farms, logging, in a warehouse and a foundry, and as "printer's devil", he learned to appreciate the school of hard knocks.
James P. Leary received his B.A. in literature from the University of Notre Dame in 1972. In 1973, he earned his M.A. in folklore from the University of North Carolina. Leary earned his PhD in folklore and American studies from Indiana University in 1977. His research focuses on the folklore of the Upper Midwest, especially Scandinavian Americans, indigenous and immigrant people, and rural and working-class peoples. Leary teaches at the University of Wisconsin–Madison in the Scandinavian Studies Department and the Department of Comparative Literature and Folklore Studies. In 2012, he was a Fulbright Scholar in Iceland.
From 1999 to 2009, Leary served as the Director of the Folklore Program (now the Department of Comparative Literature and Folklore Studies) at the University of Wisconsin–Madison. He also co-founded, with Joseph C. Salmons, the Center for the Study of Upper Midwestern Cultures.
Leary has published articles in journals such as Journal of American Folklore, Scandinavian Studies, Journal of the Folklore Institute, and Western Folklore. He has also researched and helped produce several folk life festivals, museum exhibitions, documentary sound recordings, and films, such as The Art of Ironworking. Leary co-produced Down Home Dairyland with Richard March for Wisconsin Public Radio from 1988 to 1995.
In his book, Polkabilly: How the Goose Island Ramblers Redefined American Folk Music, Leary proposes a redefinition of traditional American folk music and proposes a new genre known as "Polkabilly".
Leary is a Fellow of the American Folklore Society. The Fellows of the American Folklore Society honor folklorists who have made outstanding contributions to the field of folklore.
Together with Thomas A. DuBois, he served as co-editor of the Journal of American Folklore.