Mary O'Brien may refer to:
Mary Ann O'Brien (born 1960), Irish politician Mary Eileen O'Brien, American academic administrator Mary F. O'Brien, United States Air Force general Mary Grace O'Brien (born 1958), judge of the Virginia Court of Appeals Dusty Springfield (Mary Isobel Catherine Bernadette O'Brien, 1939–1999), British pop singer Mary Kay O'Brien (born 1965), American politician and judge Mary O'Brien, 3rd Countess of Orkney (1721–1791), mute Irish countess Mary O'Brien, 4th Countess of Orkney (1755–1831), Scottish peeress Mary O'Brien (philosopher) (1926–1998), feminist political philosopher Mary O'Brien (writer) (fl. 1785–1790), Irish poet and playwright Mary O'Brien Harris (1865–1938), British politician