Dennis O'Neill may refer to:
Dennis O'Neill (baseball) (1866–1912), 19th-century baseball player Dennis O'Neill (manslaughter victim), British manslaughter victim Dennis O'Neill (rugby league), rugby league footballer of the 1970s for Great Britain, and Widnes Dennis O'Neill (tenor) (born 1948), Welsh tenor
See also Dennis O'Neil (1939–2020) aka Denny O'Neill, American comic book writer and editor Dennis Patrick O'Neil (1940–2003), Roman Catholic bishop Denis O'Neil (born 1936), Australian sailor