Before getting the results, here is a selection of the best pictures from this voting day.
The 41-year-old Varadkar has been Prime Minister - or Taoiseach - since 2017 when he took over the leadership of the right-wing liberal Fine Gael from Enda Kenny.
Members of the public arrive to cast their votes at St Anthonys boys school in Ballinlough, Cork.
In Dublin, a stream of voters made their way to polling stations.
A member of the public fills out their ballot paper in a booth in a Polling Station in Dublin.
If the exit poll is accurate, the outcome will pose a major conundrum for FF/FG, which have both vowed never to enter a coalition with SF, citing its historic ties with the IRA - but who will also be reluctant to give up power.
Party leader Mary Lou McDonald condemned the murder as "barbaric".
Sinn Fein's polling performance has far surpassed the expectations of party strategists who, coming off the back of several disappointing elections, only fielded 42 candidates in the race for the Dail parliament's 160 seats.
With three parties vying for the top spot in today's election, no single group is expected to gain enough seats to govern alone, and a coalition of some kind is nearly inevitable.
Fianna Fail and Fine Gael, both centre-right in outlook, have unequivocally ruled out any partnership with Sinn Fein, and for either to change position would represent a major U-turn.
Fianna Fail topped the opinion polls early in the campaign, and leader Mr Martin could yet emerge as Ireland's next Taoiseach. McDonald, a 50-year-old Dubliner, has helped Sinn Fein shed its hard-line image since replacing Gerry Adams, a Belfast native who led the party from 1983 to 2018.
Brexit did not feature prominently in a campaign that was instead dominated by domestic issues such as spiralling rental prices, record-breaking homeless numbers, controversy over the state pension age and a struggling health service. His minority government has operated through a "confidence-and-supply" agreement with arch-rival party Fianna Fail, through which it is supplied the necessary votes to pass measures on an issue-by-basis.
Analysts expected Fianna Fáil to win around 55 seats, with Fine Gael 35 and Sinn Féin taking up to 30 seats.
Alexander Faw, 22, said: "I'm looking for a more left government of Ireland".
The willingness of smaller parties such as Labour and the Greens to become a junior coalition partner could prove critical.
Since 2016, Fianna Fail has supported Fine Gael in the government with a trust and supply agreement that could involve them in the government's perceived failures.
A strong result for Sinn Fein could even force Ireland's two traditional political superpowers to contemplate the once unthinkable - a grand coalition in government together.