Mary O'Brien may refer to: Mary Ann O'Brien (born 1960), Irish politician Dusty Springfield (Mary Isobel Catherine Bernadette O'Brien, 1939–1999), British pop singer Mary K. 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 Grace O'Brien (born 1958), judge of the Virginia Court of Appeals