Taoiseach Bertie Ahern will today officially tender his resignation after 11 years as Taoiseach.
He will meet President Mary McAleese after one of his final acts in office - the opening of the Battle of the Boyne site in Co Louth with the North's outgoing First Minister Ian Paisley.
The 82-year-old Democratic Unionist Party leader is also due to step down this month.
The Taoiseach will later travel to his now famous local pub, Fagan's of Drumcondra, where he will mark the occasion with friends and neighbours, almost a week after his historic address to Congress in the US.
Mr Ahern will be succeeded by current Tánaiste Brian Cowen tomorrow when the latter will be formally nominated to the Office in the Dáil.
Mr Ahern announced his shock resignation early last month amid mounting pressure over his personal finances, which are currently being probed by the Mahon Tribunal.
Elected Taoiseach in 1997 and winning three successive General Elections for Fianna Fáil, Ahern is Ireland's second longest serving Taoiseach, after party founder Eamon De Valera.
While denying any wrongdoing, the 56-year-old said he decided to hand over the party reins earlier than expected because he did not want the focus on his finances to create problems for the ruling party.
The Taoiseach will begin his final day in office by travelling to Co Louth to jointly open the €25m Battle of the Boyne restoration project with Mr Paisley.
The scheme includes a visitor centre in Oldbridge House with exhibitions depicting the battle, audio visual facilities, the restoration of the walled gardens and a tea room and full-scale replica 17th Century artillery and military equipment.
The Protestant King William III defeated the Roman Catholic King James II at the location in 1690 - a hugely symbolic event celebrated every year in Orange Order parades across the North.
Almost a year ago the two leaders met at the site where Mr Paisley presented the Taoiseach with an antique musket rifle used by one of King James' troops at the 1690 battle.
Using original 17th Century swords the Taoiseach and the First Minister will jointly cut the ribbon this morning.
Following the official opening, the Taoiseach, the First Minister and Baroness Paisley will receive a guided tour of the visitor centre.
The symbolic ceremony is expected to be over by lunchtime and then Mr Ahern will travel the 30 miles south to Dublin to hand over his letter of resignation to President McAleese at around 6pm.
Last Sunday Mr Ahern, whose high points in office include the signing of the Good Friday Agreement in 1998 with former British Prime Minister Tony Blair, said he would continue to represent his Dublin Central constituency, but would decide in the future if he would run in the next General Election.