Sir Con Douglas Walter O'Neill GCMG (3 June 1912 – 11 January 1988) was a British civil servant and diplomat. He was the British Ambassador to China (1955–1957) and the British Ambassador to Finland (1961–1963). He was also the British representative to the European Economic Community from 1963 to 1965 and led the British delegation which negotiated the country's entry to the EEC. O'Neill died on 11 January 1988. His daughter Onora is now Baroness O'Neill of Bengarve.