Career
He wrote several books and a number of articles on Finnish folklore. He was the first to have introduced the type system of proverbs similar to the Aarne–Thompson classification system of folklore, the Matti Kuusi international type system of proverbs. With encouragement from Archer Taylor he founded the journal Proverbium: Bulletin d"Information sur les Recherches Parémiologiques, published from 1965 to 1975 by the Society for Finnish Literature, which was later restarted as Proverbium: International Yearbook of Proverb Scholarship.
During his study period in the 1930s, Matti Kuusi was involved with nationalist political organizations.
He led the effort to produce a collection of "900 Balto-Finnic Proverb Types with Russian, Baltic, German and Scandinavian Parallels", described as one of the "major multilingual proverb dictionaries". Although his personal research specialties were Finnish epic poetry and proverbs, he developed the folklore studies in Finland by encouraging research of urban legends and popular-lore.
He took also interest in African folklore.