Enda Kenny will host all-Ireland talks on the impact of Brexit within weeks.
The Taoiseach said the "all-island, all-Ireland conversation" in November will involve business people, members of civic society and political parties.
Details of the gathering will be revealed in the "near future", he told the Dáil, on its first day back after the summer break.
And he warned the process of Britain leaving the European Union could take a lot longer than some expect.
"I fear that this will run for quite some time," he said.
"It might not be as straightforward or as short-term as many people think."
The Democratic Unionist Party (DUP), Northern Ireland's largest political party, has signalled it will not take part in any all-island forum.
A party spokesman told the Press Association there was no need for new structures and that cross-border talks about Brexit could be carried out within existing arrangements.
Northern Ireland First Minister and DUP leader Arlene Foster rejected suggestions of an all-island Brexit forum at the last North South Ministerial Council meeting at Dublin Castle in July.
But under questioning from Sinn Féin leader Gerry Adams in the Dáil, Mr Kenny confirmed he was pressing ahead with the talks.
"It is my intention to convene an all-island, all-Ireland conversation about this, obviously to which business people, members of civic society and political parties will be invited," he said.
Mr Kenny said the outcome of June's referendum result had sparked a great deal of confusion and uncertainty and was a matter of the utmost seriousness and concern to Ireland's interests.
Mr Adams said the entire post-Good Friday Agreement architecture is under threat because of the "British government's insistence on dragging the people of the North out of the EU against their wishes".
A majority of voters in Northern Ireland backed remaining within the bloc.
"It is very important that we send a very clear message that the vote of the people of the North must be respected," he said.
He added: "For decades we have been lectured about respecting the majority vote in the North.
"Well here is a majority vote which says it wants to remain within the European Union and you as Taoiseach, in my opinion, have a duty and a responsibility to advocate this."
Separately, Stormont Finance Minister Mairtin O Muilleoir told a parliamentary watchdog that forcing Northern Ireland out of the EU would "breach the spirit and letter of the Good Friday Agreement".
"Dragging the North from Europe would pose a threat to the entire island," he said.
"We are all Europeans. It is our fervent wish to remain at the heart of Europe. That is how the people voted in the referendum."
Mr O Muilleoir said he was hoping to work in collaboration with the Irish government to ensure the "democratic will of the people of the North is respected".
Before the Dublin parliament's Implementation of the Good Friday Agreement committee, he also warned €120m in funding for cross-border projects was currently "stuck in the system".
British Chancellor Philip Hammond has agreed to underwrite any EU projects granted permission up to November 23, he said.
Mr O Muilleoir said Stormont officials were working hard to push through existing applications before then but needed Dublin and Brussels to do the same.
"There is a hold-up and it's not on our side," he said.