Taoiseach Leo Varadkar will reveal his no-deal Brexit plans next Thursday after the EU summit failed to produce any breakthrough on the increasingly deadlocked crisis.
Mr Varadkar confirmed the decision despite insisting that Ireland will not need an emergency second budget next year even if a no-deal creates a €3.6bn hole in current financial plans.
Speaking to reporters at the end of the two-day Brussels summit, Mr Varadkar said no one is "threatening" Britain about a no-deal and that he still believes an agreement can be struck.
However, noting the failure to make any breakthrough and joining other EU leaders in rejecting British Prime Minister Theresa May's pleas for legal or political declaration help, he said no-deal plans must now be fast-tracked.
"No matter what, we have to make preparations, so the next step now is that on December 19 the European Commission will release its legislation for a no deal. The Tánaiste [Simon Coveney] will meet the stakeholders' forum next Thursday and, after that, we will produce a further updated document from us on our domestic preparations," he said.
While the plans will be discussed by EU leaders at a special "no deal seminar" in mid-January, Mr Varadkar ruled out British hopes of an emergency summit next month.
He also said an emergency second budget will not be part of Irish no-deal plans despite an ESRI report claiming that the worst case scenario could cost Ireland €3.6bn next year, saying the existing budget has a rainy day fund and is "framed" with Brexit in mind.
Mr Varadkar separately said that while "robust assurances" have already been given to Ms May, no extra legal agreements will be provided as leaders cannot be expected to keep "coming back every couple of weeks" only to say "what are you asking for?".
The Taoiseach was speaking as Ms May told reporters that more talks will take place "in the coming days" and that she believes further concessions can be provided.
In Britain, Brexiteers warned that Ms May has failed to make any breakthroughs while UK Labour leader, Jeremy Corbyn, said the time has come for parliament to "take back control", calling for a Brexit deal vote next week which could kill off any deal.