Micheal Martin, the leader of the centre-right Fianna Fail party, said the full impact had not reached the republic yet and when it did it would alter Ireland both economically and politically.
In TheJournal.ie footage, Mr Martin claimed Brexit was “generational” and the “biggest threat to Ireland almost since our foundation”.
He said: “This is the biggest change on our economic model in post World War Two society and I sometimes think people might not get the gravity of that because it’s not something obviously that people may experience in its fullest scale and to the fullest degree in the next six months or 12 months, although the fall in sterling is impacting immediately.
“But in the broader sense this is a generational change so you just can’t look at the six month or 12 month horizon, this is something that is generational in its impact.”
Micheal Martin warned against Brexit's impact on Ireland
This is the biggest change on our economic model in post World War Two society
He added issues would amount to “much more” than possible visa exchanges between Ireland and the UK.
Basic rights on education, health and social welfare protection, which had been a “seamless interaction” between the countries needed to be sorted out in a post-Brexit world, he said.
He said: "We are not going to join the English in their desire to repeal the 20th century.
"We will not join them in their right-wing ideology of trade rules with no social dimension and no enforceable laws."
But, Ireland’s Prime Minister Enda Kenny has said it would be “deeply unwise” for the European Union to punish Britain for leaving the bloc.
He has called for a transitional agreement to ease any damage caused from the UK’s divorce from the union.
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He said: "Whether in London, Brussels, or anywhere else, talk of punishment or of cliff edges is deeply unwise and can only be harmful to everybody in Europe.”
BORDER-FREE Schengen: Countries you can visit WITHOUT a passport
Mon, January 23, 2017
If you are an EU national, you do not need to show your national ID card or passport when you are travelling from one border-free Schengen EU country to another. The Schengen Area is an area comprising 26 European states that have officially abolished passport and any other type of border control at their mutual borders.
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Mr Kenny, who has expressed his desire to work closely with the UK after Brexit, has said Ireland would fight against the launch of a hard border between the north and south as it would go against the republic’s national interest.
Meanwhile, Irish fisherman have called for Ireland to follow Britain out of the EU as they fear a hard-Brexit would kill off their livelihood.
They are worried the UK could decide to close its waters after quitting the bloc and British seas account for a third of Irish seamen’s annual catch.