Mary O'Neill

Mary O'Neill may refer to:

• Marykate O'Neil (born 1968), American indiepop 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