Dennis O'Neill

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