Conor Cruise O’Brien’s life straddled diplomacy, politics, historical scholarship, literature and journalism. He was a diplomat at the UN, a professor in the US, a government minister in Ireland, the Editor-in-Chief of The Observer in Britain and a writer whose work commanded attention throughout the English-speaking world.

He was an inveterate controversialist, the quality of whose judgment and the wisdom of whose actions were often questioned, especially in his homeland. But none could deny the force of his intellect, the skill of his exposition and the courage with which he held to his convictions.

He was born in 1917 into a family caught up in the heady political and literary life of Dublin. His mother Katherine, daughter of the Irish Party MP David Sheehy, was probably the original of Miss Ivors, a strident nationalist girl depicted in James Joyce’s short story The Dead. His father, Francis Cruise O’Brien, was a somewhat waspish journalist who disconcerted his associates by abandoning his religion and speaking with an Oxford accent. He died suddenly in Conor’s presence on Christmas Day 1927, when the boy, his only child, was 10.

O’Brien’s upbringing then became a political and religious battleground between two formidable widowed aunts, Hannah Sheehy-Skeffington, an agnostic radical whose pacifist husband had been executed on the orders of an insane British army officer during the 1916 Rebellion, and her sister, Mary Kettle, a pious Catholic, whose husband, the poet and former MP Tom Kettle, had been killed in action on the Somme.

Despite pressure from priests and some of her family, O’Brien’s mother conformed to her agnostic husband’s wish that their son should not be sent to a Catholic school. Friends, among them Joyce, clubbed together to find the fees to send him to Sandford Park, a non-denominational school where his cousin, Owen Sheehy-Skeffington, was head boy. From there the young O’Brien went on to the predominantly Protestant Trinity College Dublin.

The result was that he was educated in a minority culture, apart from the mainstream of Catholic Ireland. His accent was different. He was to remain an outsider in Irish life, widely perceived as having the superior attitude to his compatriots associated in many of their minds with Trinity and the Protestant Ascendancy.

At Trinity O’Brien read Irish and French before turning to history, and made a clean sweep of the prizes. Contemporaries thought him somewhat arrogant, though, and denied him election to the highest office in the college debating society. He took his first steps in journalism as college correspondent of The Irish Times. He also joined the Irish Labour Party — and then embarrassed it by his outspoken opposition to Franco in Spain.

Before he left Trinity he married Christine Foster, a fellow-student who was a member of a noted liberal Protestant family in Ulster.

In 1944 he entered the Department of External Affairs, as the Irish diplomatic service was described, having served for a time in the Department of Finance, whose work he found uncongenial (he had little interest in economics). In the late 1940s and early 1950s he was employed on a virulent anti-partition campaign launched by the Foreign Minister, Sean MacBride, and universally supported by Irish political leaders. This denied the right of the majority in Northern Ireland to opt out of the Republic. O’Brien ran the Irish News Agency, which spewed out propaganda. For all his later protestations, there is no evidence that he was other than enthusiastic about the policies he helped to propound.

If O’Brien subscribed fully at this stage to the irredentist national aims of the Irish State, he remained apart from the strong Catholic ethos of its people. But he was not indifferent to his ancestral faith, the influence of which on literature and politics was a constant preoccupation. He could never forgive the hurt caused to his mother by some of the Church’s rules.

In 1952, under the pen-name Donat O’Donnell, he published a book, Maria Cross, a series of essays on Catholic writers including Albert Camus, Graham Greene and Evelyn Waugh. At this time he was also engaged on a study of Charles Stewart Parnell, for which he was awarded a doctorate. Published in 1956, it placed him in the front rank of Irish historians.

After a stint at the Paris Embassy in the mid-1950s, O’Brien was appointed head of the UN section of the Department of External Affairs. Ireland had just been admitted to membership of the UN. The Foreign Minister, Frank Aiken, rejected suggestions that Ireland should align itself totally with the US and its Western allies. This was manifested in a decision to vote in favour of discussing the admission of Communist China to the UN. Since Aiken was a man of limited intellect, it was widely but wrongly assumed that O’Brien had led him astray.