Sinn Fein, formerly a fringe party due to past associations with the IRA, have come top of the popular vote and broken the 90-year dominance of Fianna Fail and current premier Leo Varadkar’s Fine Gael.
The stunning result could even have an effect on British politics and Brexit.
So, what happened?
Mary Lou McDonald’s Sinn Fein won the popular vote, with 24.5% of the vote share on first preference, beating Fianna Fail on 22.2% and Fine Gael on 20.9%.
It means Varadkar, a familiar face in the UK due to his key role in the first phase of Brexit negotiations, is highly unlikely to remain as taoiseach or even Fine Gael leader.
But Ireland’s election system means Sinn Fein will not have the most seats because it only ran half as many candidates as its nearest rivals.
A coalition government will have to be formed, with Sinn Fein likely to first try and cobble together an administration with smaller left-wing parties such as Labour and the Greens.
But a tie-up with Fianna Fail may be more realistic, although that would require Michael Martin’s party to drop its previous refusal to work with Sinn Fein.
There have been indications this could happen but the whole process is likely to take weeks.
What does it mean for Brexit?
Ireland had a key role to play in the first stage of Brexit negotiations when the central issue was coming up with a solution which maintained an invisible border with Northern Ireland.
With that now resolved, the country will still be an important player but will have a reduced role as Britain and the EU sort out their long-term trading relationship, and only 1% of Irish voters made their choice based on Brexit policy.
That said, if Sinn Fein enters government it could end up making life harder for Boris Johnson.
The party has been critical of the deal the prime minister did with Varadkar, who it believes made too many concessions.
And it will be keen to ensure Johnson keeps to the promise made in the withdrawal agreement to essentially make Northern Ireland a special economic zone, with checks on trade with the rest of Great Britain and a continued invisible border with the Republic.
This of course could help further its demands for Northern Ireland to break off from the UK and join the Republic in a united Ireland.
Jon Tonge, an expert in Irish politics at Liverpool university, told HuffPost UK: “Sinn Fein would be quite happy for goods going from Great Britain to Northern Ireland to be treated as exports because that’s an economic united Ireland.”
Denis Staunton, London editor of the Irish Times, agreed that Sinn Fein’s presence in government would make little difference to the main negotiations “because Irish issues won’t be centre stage this time and we’ll just be one of 27 member states”.
He went on: “Where it could make a difference is in negotiations about implementing the Northern Ireland protocol.
“Varadkar might have tried to persuade the EU to make things as easy as possible and to minimise the visibility and intrusiveness of the economic border in the Irish sea.
“A Sinn Fein-led government (or one where they’re equal partners with Fianna Fáil) might not be so cooperative.
“(Sinn Fein) have an interest in aligning north and south as much as possible.”
Could Sinn Fein’s victory from the left bolster Corbynites in Labour?
Labour deputy leadership candidate Richard Burgon has immediately claimed Sinn Fein’s success shows that those arguing for his own party to move to the centre “are completely wrong”.
While Varadkar tried to fight the election on his Brexit successes, voters instead made their choice based on crises in public services, including health and housing.
Sinn Fein’s proposals included a massive housebuilding project, investing in public services, and abolishing property tax.
Meanwhile, the main parties were “punished” for not ensuring good economic growth was passed on to ordinary Irish citizens.
So Tonge said there “was something” in what Burgon was saying as Sinn Fein were offering left-wing policies.
“But these were not full blooded left wing policies, the Labour party’s manifesto here was a lot more left wing,” he said.
“Sinn Fein wasn’t promising full blooded nationalisation of industries and free broadband for everyone.”
Does Sinn Fein’s victory mean the break-up of the UK and formation of a united Ireland?
Sinn Fein is not making a referendum on a united Ireland, known as a border poll, a red line for coalition talks.
But there is no doubting the reunification of Ireland is their “core business” and so the pressure will grow, Tonge said
“Sinn Fein as part of a coalition government will demand that we produce papers on Irish unity, so for the first time there will be a prospectus for a united Ireland.
“Secondly, Sinn Fein will up its demand for a border poll.”
He added: “It ups the ante in terms of pressure for Irish unity.”
Under the terms of the Good Friday peace agreement, the UK Northern Ireland secretary must call a border poll when it appears likely that a majority of the province’s voters would favour a united Ireland.
Sinn Fein’s presence in the Irish government and Johnson’s Brexit deal may make that more likely.