Simon Harris will be formally appointed as Ireland's prime minister by parliament on Tuesday, replacing Leo Varadkar after he abruptly quit last month citing personal and political reasons. 

The center-right Fine Gael party -- part of a three-party governing coalition -- selected the 37-year-old Harris as leader following an uncontested election after Varadkar's resignation. 

Pledging to re-energize and "reset" his party, Harris told a weekend conference of its members that he plans to steer it back towards "core values" like promoting business, farming, and law and order. 

Harris will become Ireland's youngest ever "taoiseach" -- a Gaelic word for "chieftain" or "leader" pronounced "tee-shock" -- beating Varadkar, who was 38 when he took the role in 2017.

Varadkar, who was in his second stint as prime minister and at 45 still one of Europe's youngest leaders, said when he resigned he felt he was no longer the "best person" to lead the country. 

"Politicians are human beings. We have our limitations," he said on 20 March in Dublin, surrounded by his Fine Gael cabinet colleagues.

"We give it everything until we can't any more and then we have to move on," he added.

Harris' crowning as prime minister caps a meteoric political rise.

He joined the youth branch of Fine Gael at the age of 16 and quickly rose through its ranks. 

A county councillor at the age of 22, he was elected to parliament as a 24-year-old in 2011.

At the time he was the youngest MP and was nicknamed "Baby of the Dail" (Irish parliament).

He was appointed health minister in 2016 aged just 29 and higher education minister in 2020.

Even critics concede he is a talented communicator.

Reshuffle

Harris's prominence on social media, especially TikTok, has made him one of the most visible politicians in Ireland. 

The new taoiseach will face a formidable to-do list, including tackling housing and homelessness crises, and criticism of government policy on asylum seekers. 

One of his first jobs will be to choose his cabinet of ministers.

Harris said last week that some contenders will be "rightly delighted", while others will "feel a sense of personal disappointment".

"I will do my very best to use the best judgment that I have in the mandate I've been given by this party to put together the best cabinet," he added.  

When he was selected last month, Harris told party's members that he would repay their faith with "hard work, with blood, sweat and tears, day in and day out, with responsibility, with humility and with civility".

He also said he would pursue a "more planned and sustainable" immigration policy, following increased tension over the issue, and that he would "fight against the dangers of populism".

With a reputation for slick communication skills, Harris will also urgently seek to galvanise his struggling party, which lags in polls as key elections loom.

Ireland votes in local and European parliament ballots on 7 June, while the next general election must be held by March 2025.

Fine Gael slumped to third place at the last general election in 2020, well behind left-wing, nationalist Sinn Fein, which secured the largest share of the vote. 

Sinn Fein -- the former political wing of the paramilitary IRA -- remained outside the governing coalition and still leads in the polls.