Sir Con O'Neill, was a British civil servant and diplomat. He led the British delegation which negotiated the country's entry to the European Economic Community.

O'Neill was the second son of Ulster Unionist M.P. Hugh O'Neill, 1st Baron Rathcavan

Hugh O'Neill, 1st Baron Rathcavan

Robert William Hugh O'Neill, 1st Baron Rathcavan PC , known as Sir Hugh O'Neill, Bt, from 1929 to 1953, was an Ulster Unionist member of both the UK Parliament and the Parliament of Northern Ireland....

. He studied first at Eton

Eton College

Eton College, often referred to simply as Eton, is a British independent school for boys aged 13 to 18. It was founded in 1440 by King Henry VI as "The King's College of Our Lady of Eton besides Wyndsor"....

, then at Balliol College, Oxford

Balliol College, Oxford

Balliol College , founded in 1263, is one of the constituent colleges of the University of Oxford in England but founded by a family with strong Scottish connections....

. He gained a fellowship at All Souls

All Souls College, Oxford

The Warden and the College of the Souls of all Faithful People deceased in the University of Oxford or All Souls College is one of the constituent colleges of the University of Oxford in England....

 in 1935 before joining the Diplomatic Service in 1936.

In 1939, with the outbreak of World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

, he entered the Army Intelligence Corps. He joined the German Section of the Political Warfare Executive

Political Warfare Executive

During World War II, the Political Warfare Executive was a British clandestine body created to produce and disseminate both white and black propaganda, with the aim of damaging enemy morale and sustaining the morale of the Occupied countries....

, during which time he would interrogate Hitler's former deputy, Rudolf Hess

Rudolf Hess

Rudolf Walter Richard Hess was a prominent Nazi politician who was Adolf Hitler's deputy in the Nazi Party during the 1930s and early 1940s...

. He left the army for the Foreign Office in 1943. During 1946 an 1947 he was a leader writer for the Times

The Times

The Times is a British daily national newspaper, first published in London in 1785 under the title The Daily Universal Register . The Times and its sister paper The Sunday Times are published by Times Newspapers Limited, a subsidiary since 1981 of News International...

. He re-entered the foreign service in 1948.

His daughter Onora is now Baroness O'Neill of Bengarve.