Taoiseach Enda Kenny has insisted on a clause in the Brexit deal to allow the North to rejoin the European Union as part of a united Ireland.
After a summit with European Commission President Jean Claude Juncker, the Taoiseach said the Good Friday Agreement must be stitched into the outcome of talks on Britain leaving the bloc.
Referring to the fall of the Berlin Wall, he said the EU divorce deal must allow for the North to "seamlessly" reunite with the Republic of Ireland if a majority votes for it.
"We want that to remain in such a position that the language of what is contained in the Good Friday Agreement will also be contained in the negotiations outcome," he said at a press conference in Brussels.
"In other words, if at some future time, whenever that might be if it were to occur, that Northern Ireland would have ease of access to join as a member of the European Union again.
"We want that language inserted into the negotiated treaty or negotiated outcome whenever that might occur."
Flanked by Mr Juncker, Mr Kenny said Europe supported the internationally recognised Good Friday Agreement peace deal, which allows for a united Ireland if democratically backed by the North.
The region voted to remain in the EU during last year's in/out referendum by 56% to 44%.
However, the largest party, the Democratic Unionist Party, campaigned for a leave vote and has insisted the overall UK result must be respected.
Mr Kenny said the language of the Good Friday Agreement speaks for itself.
"It provides for that opportunity... in respect of that situation that arose arose when the Berlin Wall was taken down and East Germany was able to join West Germany in a seamless fashion," he said.
"That is already inherent in the Good Friday Agreement, therefore in protecting that, we want that language incorporated into the (Brexit) agreement that will eventually emerge."
Mr Juncker vowed the EU and Ireland would work closely together to minimise the impact of Brexit on Irish citizens.
The EC president also explicitly declared there should be no "hard border" between Northern Ireland and the Republic of Ireland as a result of Britain's decision to leave the EU.
En route Brussels to meet BelgianPM & Pres Junker of the Commission to discuss Brexit. These discussions will become serious in months ahead— Enda Kenny (@EndaKennyTD) February 23, 2017
"We don't want to have borders between Northern Ireland and the Republic," he said.
"We want to have the Good Friday Agreement not being put at risk and we want the land border being as open as possible."
The 310-mile frontier that separates Northern Ireland and the Republic of Ireland has been virtually invisible since the peace process.
Debate on both sides of the border has raged over whether a "hard" or "soft" border will result from the EU pull-out and the possible fall-out for peace, trade and freedom of movement on the island.