The Taoiseach has said there will have to be a transition period after Britain leaves the European Union, during which a full legal framework for a new relationship between Britain and the EU can be worked out.
In a major policy speech on Brexit, Enda Kenny said there needs to be a parallel process of talks on that future relationship, running alongside the Article 50 talks that will set the terms for Britain's departure from the EU.
He also firmly rejected any suggestion that Ireland should leave the EU, saying: "The foundation of Ireland's prosperity and the bedrock of our modern society is our membership of the European Union. That will not change."
Likening the Northern Ireland border to the Berlin wall, and calling it "one of the most divisive borders in the world", Mr Kenny said it is a "matter of vital national interest for Ireland that we do not return to the days of a hard border we knew only too well".
He said not returning to the old border - or creating a new one in the future - is a political matter, not a legal or technical matter.
It will have to be solved by political leadership, he said.
The Taoiseach said without the European peace process represented by the Treaty of Rome, there could have been no Good Friday Agreement.
"I am in absolutely no doubt that the European Union, which has done so much to support reconciliation on this island, will defend the peace process and the Good Friday Agreement."
Describing Brexit as "a serious, direct threat to Ireland's economic prosperity", the Taoiseach said the Government will publish a new trade and investment strategy before St Patrick's Day, and will undertake the largest ever programme of ministerial trade missions this year.
There will also be an updated Enterprise 2025 strategy that will include a medium-term stabilisation and adjustment plan for those businesses that will be most affected by Brexit.
The measures will be supported by government funding where appropriate, and the Government will request EU aid where appropriate.
The State will have to "prioritise policy measures and dedicate resources to protect jobs in the sectors and regions most affected by Brexit", he said.
To succeed as an open economy and a welcoming society, Ireland must remain at the heart of Europe he added.
Membership of the single market and the customs union, he said, are absolutely fundamental to Irish economic strategy, and dismissed any suggestion that Ireland will leave the EU.
The Taoiseach said: "I utterly reject any suggestion that we would leave the European Union."
He said history has shown that Ireland must hold fast to three essential elements:
- We must remain at the heart of Europe and open to the world
- We must protect the hard-won peace on our island, and
- We must pursue thoughtful, prudent but ambitious economic policies.
He said "the Government's plan for Brexit combines these three essential elements".
The Brexit talks ahead will require skill creativity and imagination, the Taoiseach said.
He said "our negotiating objectives are crystal clear. We are firmly focused on winning the argument and on getting the best deal for Ireland.
"We will have to demonstrate toughness, patience and resilience. We will remain at the heart of the European Union and open to the world. We will protect the peace process. We will implement our comprehensive Economic Plan."
The next few years, he said, will "require a supreme national effort", but he said he was optimistic for success.
Sinn Féin leader Gerry Adams has warned that the dangers posed to the Good Friday Agreement were "enormous" if the Government continues to fail to act as a co-guarantor.
The party is proposing a motion in the Dáil calling on the Government to negotiate special status for Northern Ireland within the EU, allowing the whole island of Ireland to remain in the bloc.
The motion states that a "hard Brexit" would undermine the status of the Good Friday Agreement.
Mr Adams also criticised the Mr Kenny's earlier speech in the Mansion House, and said he had rejected the special status for Northern Ireland.
He said this was a "deep flaw" in the Government's approach which, he said, was dictated by what the British government wants.
Minister for Foreign Affairs Charlie Flanagan has rejected the motion by Sinn Féin.
He said that notwithstanding the unique circumstances on the island of Ireland, terms like "special status" give rise to serious concerns for other EU partners about precedents that might be set elsewhere.
He added that the proposal would unnecessarily distract from efforts to secure arrangements to reflect the unique situation in Northern Ireland.
He also rejected the call for a Cabinet minister for Brexit, saying it was a job for the entire Cabinet.
However, Fianna Fáil's new recruit and Brexit spokesman Stephen Donnelly insisted there should be a Brexit minister.
He said the idea that "every minister is a Brexit Minister" was contributing to the vagueness of the Government's approach.