Mary O'Neill may refer to:
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Marykate O'Neil (born 1968), American indiepop singer-songwriter
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Mary O'Neill (Canadian politician) (born 1941), Canadian member of the Legislative Assembly of Alberta
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Mary Devenport O'Neill (1879–1967), American poet
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Mary O'Neill (fencer) (born 1965), American Olympic fencer
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Mary-Anne O'Neill (born 1955), Australian politician
See also
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Mary O'Neal (disambiguation)
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O'Neill (surname)
O'Neill is an Irish surname derived from the Gaelic ''Ó Néill'' meaning "descendant of Niall". The Uí Néill dynasty were the foremost dynasty of Ulster, and all Ireland, from the 5th century throughout the medieval period, until the Flight ...
{{hndis, ONeill, Mary