The guarantee will be included in the legal text of an international treaty
The Taoiseach has rejected claims the Government “oversold” the deal that was reached with the UK on the Irish border.
The legal text of the Phase One agreement made in December is due to be published by the EU this afternoon.
Mr Varadkar has previously insisted the guarantee that there will be no return to a hard border is “rock solid and cast iron.”
The agreement allows for a back-stop arrangement whereby – if all else fails – Northern Ireland would maintain full alignment with the single market and customs union regulations that are “relevant to the avoidance of a border, North-South cooperation and the all-island economy.”
On Newstalk Breakfast this morning, the Taoiseach insisted the document that will be published today is an “international treaty” that will put the back-stop arrangement into legal effect.
“Some people were trying to suggest in last couple of weeks that we had overspun or overplayed or oversold what was achieved in December,” he said.
“I think people will see today that that charge from the opposition and others is not correct.”
Fianna Fáil has accused the Government of overselling the guarantee and claimed European negotiators were attempting a “political fudge,” by moving the backstop out of the main withdrawal agreement and into a secondary document.
On The Pat Kenny Show, the party's Brexit spokesperson Stephen Donnelly said the British side has yet to see the text:
"Some of the text will come as no surprise to the UK because they would have been involved with it or agreed to it," he aid.
"Some of it they will have had an advisory role on or input in to.
"But there is text which the UK really will be seeing for the first time."
The DUP has repeatedly voiced its opposition to any solution that would put the North on a different regulatory footing to the UK.
Mr Varadkar said there are two other options on the table and it is now up to Britain to outline how they will work if it does not wish to trigger the backstop.
“It is not okay for people, whether it is pro-Brexit politicians in Britain or people from parties in Northern Ireland to just say no now,” he said.
“It is incumbent on them if they can't accept the backstop; well then they must detail how Option A or B would work."
He noted that the majority of people in Northern Ireland supported the remain position in the referendum.
"One mistake we shouldn't make is a mistake that a lot of people seem to be making;
“It is that one of the political parties, the DUP - as important as it is and as big as it is - speaks for everyone in Northern Ireland."
“Bear in mind, most people in Northern Ireland voted to remain and the business community in particular does not want to see any new borders, either North, south, East of West.
“So let’s always bear in mind when we do talk about Northern Ireland; the majority of people in Northern Ireland did not want to leave the EU and the majority of MLAs elected to the legislative Assembly, which unfortunately is not meeting at the moment, say they want to stay in the single market and the Customs Union.”
He went on to say that he did not pay much attention to recent comments by the British Foreign secretary Boris Johnson on the Irish border, adding “when I listen to the British government, I listen to the Prime Minister."
“She is going to speak on Friday,” he said. “We spoke on the phone obviously this week.”
“I really hope that that speech that she makes on Friday will give us a greater insight into how the UK want the new relationship with the EU to work and some more detail as to how that can be achieved.
“The UK can have as close a relationship with EU as it wants to have but what it can’t do is cherrypick.
“It is not possible to say we want to be aligned the EU when it suits us and when it is to our advantage but we don’t when we don’t.”
You can listen beck to his full appearance on Newstalk Breakfast here: