Irish law states that the Dáil may not sit for longer than five years meaning it must be dissolved after that period and a general election held within 30 days.
The 32nd Dáil met for the first time in March 2016 so the next general election was due to be held early next year.
But few expected this minority government to last the full five years.
The Taoiseach previously stated he would have preferred a May 2020 general election.
But Mr Varadkar told Fianna Fáil leader Micheál Martin before Christmas that the tight Dáil numbers meant it may not have been possible to avoid an immediate election unless Fine Gael was given guarantees it will be supported.
Fianna Fáil TD John McGuinness had said that he would vote against the Government rather than abstain in any no-confidence vote in the Government or a minister.
Another headache was that Fine Gael's Cork North Central TD Dara Murphy quit the Dáil further undermining support.
Mr Martin rejected Mr Varadkar's warning his party must vote in favour of Fine Gael in the Dáil, as distinct from abstaining.
Instead Leo Varadkar decided not to gamble and wait for the possibility of a motion of no-confidence being successful.
He has decided the country will go to the polls, but it’s the president who actually has the power to dissolve the government in order for a general election to be held.
Leo Varadkar must have the support of the majority of the members of the Dáil before he makes that trip to "the Park". If he does not have backing of TDs, Micheal D Higgins may refuse to dissolve the Dáil.
If and when the Áras gives the green light to bring the current government to an end, an election must be held within 30 days.
The Clerk of the Dáil issues a writ to the returning officer in each constituency directing them to hold an election of the prescribed number of members.
It’s then up to the Minister for Housing, Planning and Local Government, in this case Eoghan Murphy, to name polling day which must be between the 18th and 25th day (excluding Good Friday, Sundays and public holidays) after the issue of the writ.
The minister must also appoint the polling period, which must consist of at least 12 hours between 7am and 10.30pm.
Once polling day is named, it’s on your marks, get set, go! for the candidates to contest the Dáil Éireann seats that are up for grabs. There were 158 seats in the 32nd Dáil and there will be 160 in the next one to reflect the growing population.
The Ceann Comhairle Seán Ó Fearghaíl who is a Fianna Fáil member will be re-elected automatically.
According to the State body Citizens Information, if you wish to seek membership of the Dáil, you need to be a citizen of Ireland, be over 21 years of age, be not disqualified from election to the Dáil.
A nomination paper must be completed and given to the returning officer of the constituency in which you wish to be nominated.
It must be submitted to the returning officer for your constituency by 12 noon on the seventh day after the issue of the writ by the Dáil to the returning officer.
Then there’s the race for the other poles - the ones where the campaign posters go. But remember- written permission is needed from the owner of the pole if it’s in a public space, usually a local authority.
Posters can be erected 30 days before the election or from the date of the polling day order for the election.