Leach obtained an Master of Arts in 1917, from Johns Hopkins University in Baltimore, Maryland. His thesis predictably involved the study of literature and folklore, and dealt with the legend of the Holy Grail. For several years after graduation, he taught courses at Johns Hopkins in Early English and Medieval Literature.
A great supporter of the theory that much early literature was closely related to, or even originated in, popular folklore, MacEdward Leach believed that certain traditional, orally transmitted tales or epics should receive the same degree of scholarly attention and respect accorded to literature. While he maintains a distinction between "folk" and "sophisticated," this respect for the well-told tale can be heard in his comments regarding the Ulster Cycle tale, "Deirdre of the Sorrows":
"The great art of the Deirdre story…is a magnificent combination of folk art -- the simple concrete picture -- with the beautiful structuring and psychological motivation of sophisticated art" (Leach, "Malcolm Arnold and Celtic Magic").
In the 1920s and 30s, the University of Pennsylvania began offering courses in folklore, taught through the Department of English. Leach's background in the study of medieval texts, combined with his bourgeoning interests in folklore, made him a perfect candidate for doctoral study within this department. While a student at the university, he had the opportunity to study under the Americanist, Cornelius Weygandt and anthropologist, Frank Speck, who was himself interested in the collection and preservation of traditional lore. He completed his doctorate, which dealt with the use of Celtic tradition in literature, at the University of Pennsylvania in 1930.
Following the completion of his doctorate, MacEdward Leach taught courses in folklore within the Department of English at Pennsylvania and was widely regarded as a charismatic lecturer with a flare for storytelling. He is regarded as being instrumental in bringing the American Folklore Society back from the brink of financial collapse and nurturing its growth into an active hub of intellectual activity. He remained Secretary Treasurer of the Society from 1943 to 1960 and President from 1960 to 1962. Also to Leach's lasting credit is the establishment of a Folklore Department at the University of Pennsylvania in 1962. This department was so well respected amongst scholars that it rivaled the prestige of the established University of Indiana Folklore Department. MacEdward Leach remained at the University until his retirement in 1966, after which he returned to live in the Illinois countryside.