Cornelius O'Brien may refer to:
Cornelius O'Brien (piper) (fl. 1656), Irish musician Cornelius O'Brien (bishop) (1843–1906), Canadian Roman Catholic priest, archbishop, and author Cornelius O'Brien (County Clare) (1782–1857), politician and builder of O'Brien's tower Cornelius J. O'Brien (1869–1954), vaudeville and minstrel show performer