Oscar O'Brien (7 September 1892 – 20 September 1958) was a Canadian folklorist, composer, pianist, organist, music educator, and Roman Catholic priest. A large portion of his compositions were based in folklore and he also arranged and harmonized roughly 400 French and Canadian folksongs; many of which were written for his collaborations with Charles Marchand and the Alouette Vocal Quartet. He worked as an arranger or accompanist on numerous 78 rpm recordings for such labels as Bluebird, Brunswick, Columbia, Starr, and Victor. He contributed numerous articles on folklore to publications like Le Canada français and was a frequent lecturer on folklore subjects. In 1978 CBC Radio recognized O'Brien in a series of six broadcasts featuring his harmonizations.