Fianna Fáil leader Micheál Martin says he believes a rush to hold a 'border poll' in Northern Ireland could delay any potential Irish unity in the future.
He suggested it's important not to conflate Brexit with the question of Irish unity, and that he doesn't see a poll happening in the lifetime of the next Irish government.
Deputy Martin also argued that a 'middle ground' appears to be emerging in Northern Ireland, and that politicians should now wait and see where that takes them.
He said: "The whole 'border poll' [idea] was a Sinn Féin thing, immediately after Brexit.
"I'm interested in unifying people on this island - that's my passion. But I want to do it logically, and in agreement with the people.
"The first phase is to demonstrate that you can work that parliament and executive that's established by the Good Friday Agreement.
"Before you want to talk about new institutions or new approaches, you've got to demonstrate you can work the existing ones - and they haven't."
Deputy Martin suggested he believes in an "evolutionary pathway" rather than a sudden decision to hold a poll.
He argued: "I think the Executive should be restored, and the Assembly should be restored... Some people just want to brush all that aside and 'let's have a poll now'.
"We already see people's attitudes are changing. Far better to evolve people's thinking on this, in my view, rather than just forcing the pace on a short-term border poll - which would create all sorts of tensions, and I think could have a negative impact on unifying people."
The Fianna Fáil leader added: "I don't see it happening within the lifetime of the next government, but I could be wrong."
Reacting to Deputy Martin's comments, Sinn Féin's Pearse Doherty accused Fianna Fáil of 'abandoning any pretence of representing Republican values'.
The Sinn Féin TD claimed: “At a time when the demand for Irish unity is growing, it is time for the Irish government to begin meaningful engagement with the British government to arrange a date for a referendum on Irish unity in the north within five years - as well as putting in place plans for a referendum in this State; in line with the provisions of the Good Friday Agreement.
“It is time the people had their say and it’s time we started planning for their verdict.”
