Simon Harris has been elected as taoiseach (Irish prime minister) by members of the Dáil (Irish parliament).
Aged 37, the new Fine Gael party leader is the youngest person to lead the Republic of Ireland.
It follows the resignation of his predecessor Leo Varadkar who announced he was stepping down last month.
Mr Harris was elected after a vote in which 88 Dáil members supported him while 69 voted against his appointment.
He was officially installed as taoiseach on Tuesday afternoon after travelling to meet President Michael D Higgins to receive the seals of office.
Mr Harris was the only candidate to seek the party leadership after Mr Varadkar's shock resignation announcement in March.
Speaking in the Dáil, the new taoiseach described his election as a “very special day”.
“I accept this new role in a spirit of humility, ready for the challenge and full of energy and determination about what can be achieved,” he said.
He added that Ireland must never take peace for granted and he pledged to guard and honour his role “as protector and guarantor of the Good Friday Agreement”.
Mr Harris also vowed to lead the coalition government in a spirit of “unity, collaboration and mutual respect”.
His Fine Gael party is in a coalition with Fianna Fáil and the Green Party, but a general election is due by March 2025.
Mr Harris said he wanted the government to run for a full term, indicating he was not planning on going to the polls any sooner.
However, as it is the third time the coalition government has changed its taoiseach in less than four years, opposition parties have called for an early election.
Schoolboy error
Mr Harris has represented the Wicklow constituency for more than two decades, but he was very young when he entered elected politics.
Dáil members laughed on Tuesday when the current Social Protection Minister Heather Humpreys recalled her first impression of him in the Dáil back in 2011.
“I saw this young lad walking around the place and I said to myself: ‘Ah, sure he must be on a school tour or on work experience'.”
But Ms Humpreys said it was clear from his first day in the chamber that Mr Harris would “go far” and she added that it was her “great honour” to propose him as taoiseach.
Members of the Harris family, including his wife and two young children, were in the Dáil to witness his election.
During his first speech, he thanked his wife and promised his children that “being your dad will remain my most important job”.
‘Pass the parcel'
However, Mr Harris and his government came in for a lot of criticism during Tuesday's vote.
Sinn Féin president and leader of the opposition Mary Lou McDonald repeated her call for a fresh election, claiming Mr Harris had “failed” his way to the top.
In the Dáil, she accused the coalition government of playing “pass the parcel with the keys to the taoiseach's office” and clinging to power “at all costs”.
Speaking later to BBC News NI, Ms McDonald said it was time for the people to have their say on who should lead the Republic of Ireland.
Tánaiste (Deputy PM) Micheál Martin, leader of Fianna Fáil, defended the record of the three-party coalition.
He said the government, which came to power in June 2020, had been formed “in the middle of the greatest public health crisis in modern times”.
“We are three separate parties that seek to work together, respecting both our differences and an agreed approach to the most urgent issues facing our country,” he said.
Green Party leader Eamon Ryan said he disagreed with calls for an early general election because there was work to be done.
However, representatives of other opposition parties also said that a change of government was badly needed.
Labour Party leader Ivana Bacik said of Mr Harris that “his elevation today will not deliver the change that we need”.
Social Democrats leader Holly Cairns said Ireland was “facing serious challenges as a country and in order to address them we need new ideas”.
Aontú leader Peadar Tóibín said the Irish people had been “locked out of the decision-making process”, while People Before Profit's Richard Boyd Barrett accused Fine Gael of being afraid to face the electorate.
Congratulations
UK Prime Minister Rishi Sunak congratulated Mr Harris in a message on X, formerly known as Twitter.
“As the closest of neighbours, I look forward to forging even stronger ties between our two countries so we can deliver for people across these isles,” Mr Sunak wrote.
Keir Starmer, leader of the opposition in the UK, said: “On behalf of the UK Labour Party, I wish him well and look forward to working together as we seek to strengthen the ties of friendship between our two countries.”
Northern Ireland Secretary Chris Heaton-Harris said he looked forward to them working together “as we further strengthen UK-Ireland cooperation”.
Who is Simon Harris?
Mr Harris was born in 1986 and grew up in the coastal town of Greystones in County Wicklow.
At 37 he is a year younger than Mr Vardadkar was when he became taoiseach in 2017.
He is the eldest of three children, the son of a taxi driver and a special needs assistant.
His younger brother Adam is autistic – a fact which Mr Harris said kickstarted his own involvement in political campaigning when he was just 16.
He entered the Dáil in 2011 at the age of 24 – making him the youngest TD in chamber at the time.
He had a rapid rise through the party ranks, landing his first cabinet role before his 30th birthday.
As minister for health, he oversaw the Republic's vote to overturn its abortion ban and was in charge of the country's initial response to the Covid-19 pandemic.
Why is there a new taoiseach?
On 20 March, Leo Varadkar caused shock when he announced he would be stepping down as Fine Gael leader immediately, and would resign as taoiseach as soon as his successor was selected.
He said he was resigning for “personal and political reasons” and was no longer the best person for the job.
Mr Varadkar's resignation paved the way for a party leadership contest, but as he headed the current coalition government in Dublin, his successor was also expected to take over as taoiseach.
Mr Harris vacated his role as minister for further and higher education and has appointed former junior minister Patrick O’Donovan as his replacement.
Peter Burke has been appointed minister for enterprise, trade and employment, replacing Simon Coveney who announced his intention to resign last week.
Mr Harris has left the rest of his Cabinet unchanged.
