The architects of the Good Friday Agreement will gather in Belfast later.
Former US president Bill Clinton, ex-British Prime Minister Tony Blair and former Irish Taoiseach Bertie Ahern will be among those marking the 20th anniversary of the landmark deal at Queen's University in Belfast.
It largely ended the 30-year sectarian conflict which claimed more than 3,000 lives and was codified by the British and Irish Governments with the agreement of most of the major Stormont parties with the notable exception of the Democratic Unionists.
The accord included the early release of around 500 paramilitary prisoners within two years even though IRA arms had not yet been destroyed.
Prisoner releases almost torpedoed the agreement in the final frantic hours prior to its signing on April 10 1998 - Good Friday.
The deal also covered the re-establishment of devolved power-sharing at Stormont, establishment of cross-border political bodies with the Republic, and led to the root and branch reform of the Royal Ulster Constabulary (RUC) into the Police Service of Northern Ireland (PSNI).
Paramilitaries undertook to destroy weapons and the IRA did so in 2005.
It enshrined the principle of consent - that Northern Ireland's constitutional position as part of the UK would only ever change if a majority in the region voted for it - while at the same time offering provisions that legitimised nationalist aspirations to strive for a united Ireland.
The Agreement won the overwhelming support of a majority following referendums on both parts of the island and served as a blueprint for how to solve conflict around the world.
Twenty years later a ministerial Executive at Stormont has not sat for more than a year in a dispute over the status of the Irish language.
The chairman of the 1998 talks US envoy to Northern Ireland George Mitchell, former Downing Street chief of staff Jonathan Powell, ex-Sinn Fein president Gerry Adams and former Ulster Unionist leader Lord David Trimble will also be present at Queen's University on Tuesday.
Later, Mr Clinton and Mr Mitchell will receive the freedom of the city of Belfast in a special ceremony at City Hall.
On Monday Mr Clinton urged compromise and warned that stalemates could continue for only a limited period.
Mr Mitchell said peace should not be taken for granted.
Mr Blair said the most difficult meetings he had were with the victims as he wrestled with his conscience over the early release of paramilitary prisoners.
Mr Clinton said: "No one will drop off the face of the Earth with any of the reasonable compromises that have been discussed.
"The only thing that would be calamitous would be to let the whole thing die.
"To confine ourselves to purgatory or go back to hell instead of going into a futu