Gerry Adams is set to step down as Sinn Féin president later, as the party he has led for almost 35 years installs Mary Lou McDonald as his successor.
Mr Adams, 69, announced his intention to quit the role in November in a move that signalled a generational shift in the Sinn Féin leadership.
Ms McDonald, 48, will be formally elected as leader during a special ard fhéis (party conference) in Dublin.
Michelle O’Neill, 41, will also be installed as Sinn Féin vice president.
Saturday’s elections are a formality as both women ran unopposed for the leadership roles.
Mr Adams is one of the most prominent and controversial Irish politicians and his political legacy will divide opinion sharply.
Speaking on Friday night, he said he was “confident” that the new leadership would “help make Sinn Féin even bigger and stronger in the time ahead”.
“Fifty years ago when I joined Sinn Féin, it was a banned party,” he said.
“The nationalist people of the north had been abandoned and were subject to discrimination and inequality. We were on our knees. We are now off our knees.
“We have a Good Friday Agreement. It is in some difficulty at this time. But it offers the way forward.”
The leadership change comes almost 20 years after the 1998 Good Friday Agreement, but it also comes at a time of great political uncertainty.
Northern Ireland has been without a devolved government since Martin McGuiness quit as deputy first minister in January 2017, in a move which caused the assembly to collapse.
He pulled Sinn Féin out of its power-sharing coalition with the Democratic Unionist Party (DUP), objecting to their handling of a scandal over green energy scheme.
Several rounds of talks aimed at restoring devolution have failed, but there is now growing speculation that a deal could be unveiled as early as next week.
Ms McDonald and Mrs O’Neill have been present all week at talks in Stormont which have been described as a last ditch attempt to restore power-sharing.
Mrs O’Neill has been the party’s leader north of the Irish border for just over a year, having taken over from the late Martin McGuiness in January 2017.
With Sinn Féin sources saying that the talks are at crucial stage, there will be a lot of interest in what both of the new leaders will say about the ongoing negotiations.
Those talks are taking place against the complicated backdrop of Brexit and the way it impinges on economic and political matters, both in Anglo-Irish relations and in cross-border co-operation.
Mr Adams is not expected to address the gathering in Dublin’s RDS that is due to be attended by up to 2,000 delegates.
However, as he left the Stormont talks on Friday night – for the last time as Sinn Féin leader – he said: “It isn’t sorted out as we speak.
“We have made some progress but there are still considerable obstacles. But, as I said to our unionist friends, this is the last chance agreement.”
In her first speech as Sinn Féin leader, Mary Lou McDonald is expected to say she wants an ambitious plan to build and modernise the party, as it seeks to get into government north and south of the Irish border and bring about its ultimate ambition of a united Ireland.
Mrs McDonald is also expected to re-iterate Sinn Féin’s support for repealing the Republic of Ireland’s 8th amendment to the constitution that gives equal rights to life to the mother and to the unborn.
Last month, the Irish government announced it would hold a referendum at the end of May on whether to reform the country’s near-total ban on abortion.
Sinn Féin is expected to debate at its 2018 ard fhéis whether to support a proposal for unrestricted access to abortion during the first 12 weeks of pregnancy.