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
edit- Dennis O'Neil (born 1939; died 2020) aka Denny O'Neill, American comic book writer and editor
- Dennis Patrick O'Neil, Roman Catholic bishop