The leader of Ireland's chief Opposition party said he hopes Brexit will move Ireland closer to reunification.
Micheal Martin said a "reunification referendum" should be called if it becomes clear a majority want to see an end to Irish partition over the UK decision to pull out of the EU.
The Fianna Fail leader added that Northern Ireland's 56% majority vote to remain within the bloc could be a defining moment for the region.
He made his remarks delivering the annual John Hume lecture at the MacGill Summer School in Glenties, Co Donegal.
"It may very well be that the decision of Northern Ireland to oppose the English-driven anti-EU UK majority is a defining moment in Northern politics," he said.
"The Remain vote may show people the need to rethink current arrangements.
"I hope it moves us towards majority support for unification, and if it does we should trigger a reunification referendum."
But Mr Martin added: "However at this moment the only evidence we have is that the majority of people in Northern Ireland want to maintain open borders and a single market with this jurisdiction, and beyond that with the rest of Europe."
The 310-mile frontier that separates the island of Ireland is the only land border between the UK and the rest of the EU.
Although heavily militarised with checkpoints and road closures during the Troubles, the peace process has opened up a seamless crossing between both jurisdictions.
Tens of thousands pass over the border every day on their way to work, for shopping or on day trips.
Concerns about its status after the Brexit result - and whether free movement of people, goods and services will be impacted - have dominated political debate since the poll.
During the referendum campaign, Theresa May indicated some form of border control would be required in Ireland if the UK voted to leave the EU.
But just last week, Northern Ireland's new Secretary of State James Brokenshire insisted he does not want to see a hardening of the border.
Mr Martin, a former foreign affairs minister whose party is leading opinion polls and whose backing is needed by the minority Fine Gael government, said any "new barriers between both parts of this island would potentially set us back decades".
"The most urgent thing which is required is an immediate end to the hands-off detachment of recent years," he said.
"It is a sad reality that our government and our media have tended to ignore Northern Ireland except when there is a crisis.
"Meeting the challenge of Brexit is a moment to end this and also to begin rebuilding public faith in politics."
Mr Martin called for an all-island response to Brexit that reaches out "to excluded groups, to show that a broader range of interests than those articulated by the dominant political parties can be heard".
He added: "I have in particular stressed our belief that civil society must be included together with business, unions and professional organisations."