It now looks nearly certain that no party can win the simple majority in the election as the latest polls repeatedly suggested that none of the three major political parties in the country, namely Fine Gael, Fianna Fail and Sinn Fein, can get a support rate of more than 30 percent in the election.
Polls opened across the country at 0700 GMT, although a small number of islands off the west coast voted on Friday to allow for rough seas that could disrupt the transport of ballots by boat.
Varadkar had hoped the economic upturn his party has overseen since 2011 and his own diplomatic successes on Brexit - helping prevent a hard border on the island of Ireland after Britain's departure from the European Union - would extend his near three-year premiership.
Despite Sinn Fein's polling lead, it is only fielding 42 candidates - not enough to form a majority government in the lower house of parliament the Dail even if all its candidates were to win.
Sinn Fein is a major force in Northern Ireland, which is part of the United Kingdom, but has always been a minor political player in the Republic, shunned by the bigger parties because of its ties to the IRA.
A new confidence and supply deal can not be ruled out - potentially a reverse of the last one with Fine Gael supporting a Fianna Fail led-minority.
The polls close at 10.00pm, United Kingdom time, and will be followed by an exit poll giving the first indication of the result.
Fine Gael and Fianna Fail have been keen to remind the electorate of Sinn Fein's historic IRA links and as the campaign entered its latter stages the past crimes of the provisional movement drew increasing focus.
Counting begins on Sunday morning, with the first results expected to be announced in the afternoon.
Since 2016 Fianna Fail have propped up Fine Gael in government with a confidence and supply arrangement that could implicate them in the perceived failings of the government.
"(The young people) blame the current government and the coalition of parties in the government for this disaster", said O & # 39; Halpin about the housing shortage.
Sinn Fein is unlikely to form the next government as both major parties refuse to work with them.
Varadkar's party has been in government since 2011.
Despite its opinion poll lead, Sinn Fein - which wants to unite Northern Ireland with the Republic - is only fielding 42 candidates and can not form a majority government even if they all win.
"We're seeing a version of what we've seen elsewhere, a growing constituency, particularly among younger voters and those who feel left behind that the neoliberal agenda has not worked for them", said David Farrell, professor of politics at University College Dublin.
"The gains that Sinn Fein is making are consistent with what we are seeing in other democracies".
She said: "I went for Sinn Fein this time because I really do believe it's time for change".