Mary O'Neill may refer to: Marykate O'Neil (born 1968), American indie pop singer-songwriter Mary O'Neill (Canadian politician) (born 1941), Canadian member of the Legislative Assembly of Alberta Mary Devenport O'Neill (1879–1967), American poet Mary O'Neill (fencer) (born 1965), American Olympic fencer Mary-Anne O'Neill (born 1955), Australian politician
See also Mary O'Neal (disambiguation) O'Neill (surname)