The nationalist Sinn Fein party is unlikely to enter government, with opinion polls pointing to the main opposition Fianna Fail winning most seats and forming a coalition or minority government.
Fianna Fail’s policies on the economy and post-Brexit are broadly similar to those of Varadkar’s centre-right Fine Gael.
“I think there is a bit of a backlash coming (against Varadkar) from chatting to friends and colleagues,” said Shane Sullivan, a 31-year-old data analyst who voted for Fianna Fail because he wanted a focus on public spending rather than tax cuts. “I think they are just a bit out of touch to be honest.” Left-wing Sinn Fein, which has moved on from the long leadership of Gerry Adams and is run by a new generation of politicians led by Mary Lou McDonald, could win the popular vote if the vote reflects the polls. On Monday, the former political wing of the Irish Republican Army (IRA) was polling at 25%, ahead of Fianna Fail on 23% and Fine Gael on 20%.
But Sinn Fein, which has appealed to younger voters on the defining issue of the election - the cost and availability of housing - has put forward too few candidates to capitalise, as the groundswell of support caught the party itself off guard after it sunk to 9% at local elections last year.
Analysts say it may only be able to gain a few seats and retain its position as the third largest party in parliament.
While both Fianna Fail and Fine Gael insist they will not govern with Sinn Fein, citing its IRA past and differing economic polices, such an outcome would demonstrate an appetite for change in decades-long centrist Ireland.
The IRA fought against British rule in Northern Ireland in a 30-year conflict in which some 3,600 people were killed before a 1998 peace deal. Sinn Fein’s ultimate aim is to unify Ireland and British-run Northern Ireland, where it shares power.
“I went for Sinn Fein this time because I really do believe it’s time for change,” said Siobhan Hogan, a 40-year-old childcare worker, who cited Fine Gael plans to increase the pension age and its failure to solve a housing crisis.
“I’m lucky enough to have my own place but I look around and I see people struggling. People need a roof over their heads.”
Polls close at 2200 GMT and will be followed by an exit poll giving the first indication of the result. Counting begins at 0900 GMT on Sunday with some results expected from the early afternoon.
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 EU - would extend his near three-year premiership.
The strategy appears to have fallen flat amid domestic issues such as healthcare and housing.
The immediate beneficiary looks set to be Fianna Fail leader Micheal Martin, a 59-year-old former teacher whose party suffered an electoral collapse nine years ago after the government he was a member of had to seek an EU/IMF bailout.