Hillery, though not himself political, agreed under pressure from Clare's senior Fianna Fáil TD, party leader and former Taoiseach, Éamon de Valera, to become his running mate at the 1951 general election.

Under Lemass, many party elders such as James Ryan, Seán MacEntee and Paddy Smith, retired and a new generation of politicians were introduced to government, such as Brian Lenihan, Donogh O'Malley, Charles Haughey and Neil Blaney.

While Donogh O'Malley, has received much of the credit for introducing free education, it was in fact Hillery who laid much of the groundwork before this landmark announcement.

He earned an international profile when, in the aftermath of the killing of fourteen unarmed civilians in Derry, by British paratroopers (known as Bloody Sunday), he travelled to the United Nations to demand UN involvement in peace-keeping on the streets of Northern Ireland.

During the whole period, Hillery remained one of Jack Lynch's staunchest allies in pursuing peaceful means with regard to the possibility of a civil war breaking out.

As Social Affairs Commissioner, Hillery's most famous policy initiative was to force EEC member states to give equal pay to women.

However, fate took a turn, when the then Minister for Defence, Paddy Donegan, launched a ferocious verbal attack on the then president, Cearbhall Ó Dálaigh, calling him "a thundering disgrace" for referring anti-terrorist legislation to the Supreme Court of Ireland to test its constitutionality.

Fine Gael and Labour decided it was unwise to nominate a candidate, in light of the row over Ó Dálaigh's resignation and the part the government played in the affair.

Though once voted the world's sexiest head of state by readers of the German Der Spiegel magazine,[8] few expected Hillery to become embroiled in a sex scandal as president.

[9] Yet, one occurred in September 1979, when the international press corps, travelling to Ireland for the visit of Pope John Paul II, told their Irish colleagues that Europe was "awash" with rumours that Hillery had a mistress living with him in Áras an Uachtaráin (the presidential residence), that he and his wife were divorcing and he was considering resigning from the presidency.

Once the Pope had left, Hillery held a press conference where he told a shocked nation that there was no mistress, no divorce and no resignation.

Hillery, however, defended his action by saying that it was important to kill off the story for the good of the presidency, rather than allow the rumour to circulate and be accepted as fact in the absence of a denial.

In January 1982, the Fine Gael-Labour Party coalition government of Taoiseach Garret FitzGerald lost a budget vote in Dáil Éireann.

Hillery regarded such pressure as gross misconduct, and ordered one of his aides de camp, Captain Anthony Barber, not to pass on any telephone calls from opposition figures.

Three candidates had been nominated in the 1990 presidential election: the then Tánaiste, Brian Lenihan from Fianna Fáil (heavily tipped as the certain winner), Austin Currie from Fine Gael and Mary Robinson from the Labour Party.

In October 1990, Lenihan changed his story, claiming (even though he had said the opposite for eight years) that he had played "no hand, act or part" in pressurising President Hillery that night.

Having been re-elected unopposed in 1983, Hillery (until then) shared the distinction with Seán T. O'Kelly and Éamon de Valera of serving two full terms as President of Ireland.

In 2002, state papers released by the British Public Record Office under the thirty-year rule,[b] published in the Irish media, revealed how Hillery was viewed.

A briefing paper – prepared for the Foreign Secretary, Sir Alec Douglas-Home, and the Secretary of State for Northern Ireland, William Whitelaw – observed about Hillery, then Minister for Foreign Affairs: Dr Hillery is regarded as a powerhouse for ideas, one of the few members of Fianna Fáil who has new policies and is eager to implement them.

Policy in this field is determined primarily between him and the Taoiseach; and it is likely that the Fianna Fáil new line on the North owes much to Dr Hillery.

Today, we detect his foresight and pioneering agenda everywhere – a free education system, a dynamic, well-educated people, a successful economy and a thriving membership of the European Union, one of the single most transformative events for this country.

"[16] Taoiseach Bertie Ahern said he "was a man of great integrity, decency and intelligence, who contributed massively to the progress of our country and he is assured of an honoured place in Ireland's history".

[18][19] In the graveside oration, Tánaiste Brian Cowen said Hillery was "A humble man of simple tastes, he has been variously described as honourable, decent, intelligent, courteous, warm and engaging.