Born in Dublin and educated at Sandford Park and Trinity College Dublin where an outstanding undergraduate and postgraduate career culminated in the award of the PhD degree in 1954. He had joined the Civil Service after graduation in 1942 and from 1944 served in the Department of External Affairs including a period in the Irish Embassy in Paris and the Managing Directorship of the Irish News Agency. From 1956 he was in charge of the United Nations section of External Affairs and a member of the Irish delegation to the general assembly. At the request of Secretary General Dag Hammarskjöld, he was released by the Department and appointed UN civilian representative in the Congo where he had responsibility for the implementation of resolutions on the secession of Katanga. He resigned from this post and from the Civil Service in December 1961.

In 1962 he married the poet Máire Mac An tSaoi, his second wife, and accepted the position of Vice-Chancellor of the University of Ghana. From 1965 he was Schweitzer Professor of Humanities at New York University. He returned to Dublin in 1969 and was elected TD for the Labour Party in the Dublin North-East constituency, acting as party spokesman on foreign affairs. He was Minister for Posts and Telegraphs in the coalition government, 1973–77, was elected to the Seanad in 1977 after losing his Dáil seat and was editor- in-chief of the Observer newspaper, 1979–81. He has served as a Visiting Fellow at Nuffield College, Oxford, 1973–75, Fellow of St Catherine’s College, Oxford, 1978–81, Montgomery Fellow at Dartmouth College, 1984–85, and has been Pro-Chancellor of Dublin University since 1973. He has been awarded honorary degrees by a number of universities including Ghana, Edinburgh and the Queen’s University, Belfast.

His publications include Maria Cross (1952), Parnell and his party (1957), To Katanga and back (1962), States of Ireland (1973), The Great Melody (1992) and Memoir: my life and themes (1998).