Fianna Fail are to organise in Northern Ireland, Irish Prime Minister Bertie Ahern has confirmed.
Bertie Ahern's Fianna Fail intend to organise in Northern Ireland
It is the first time in the party's 81-year history that efforts have been made to mobilise on an all-Ireland basis.
Mr Ahern said Foreign Affairs Minister Dermot Ahern would chair a committee to implement the move.
"This move reflects the dramatic changes we have seen across the island," the party leader said.
Dermot Ahern said the party did not intend to contest any seats in a Westminster election.
"We wouldn't be interested in going to the House of Commons as a political party. That is for others to do," he said.
"We feel we should have representation in Northern Ireland as a political party."
Earlier on Monday, the SDLP refused to rule out a possible merger with Fianna Fail and party leader Mark Durkan later welcomed the decision to organise in the north.
"As a true republican party, we believe that the social and economic interests of the people of the entire island are best served by ever-deepening co-operation between north and south.
"We anticipate a healthy and forward-looking debate as a means to forging a new political path for the whole country," Mr Durkan said.
Sinn Fein's John O'Dowd also welcomed Fianna Fail's decision.
"Unfortunately, it has taken Fianna Fail this long to embrace the positive aspects of developing its party throughout the 32 counties," he said.
"But we are encouraged that the taoiseach has now finally acknowledged the importance of such a move."
However, Ulster Unionist leader Sir Reg Empey said the decision was "unwise and unhelpful".
"The last thing we need is another abstentionist party organising here," Sir Reg said.
"Bertie Ahern at a stroke has transformed himself from a potential partner in the process of normalisation, to a rival."
Commentators have said that Fianna Fail's plans to organise in Northern Ireland have been spurred on by the setting up of a powering-sharing executive at Stormont, making such a move less politically sensitive.
It has also been suggested that its success against Sinn Fein in the Republic's recent election played a part.