Micheal Martin has formally become Taoiseach during a ceremony with the Irish president, Michael D Higgins.
Earlier, Mr Martin said he was “thankful” to his supporters after he received the backing of the Irish parliament to be nominated as the country’s next premier.
Parliamentarians voted 95 to 76 in support of the nomination of the Fianna Fail leader, the day after a chaotic row disrupted the process and resulted in the suspension of the Dail.
Fianna Fail leader Micheal Martin leaves Leinster House (Liam McBurney/PA)
Speaking after he was nominated for the role, Mr Martin said: “It is a profound honour to be nominated to serve as head of the government in a free, democratic and diverse republic.
“Today, I am deeply conscious of the democratic tradition which our country has developed over more than a century.
“We should never take for granted the freedoms and opportunities secured for us by the generations who sat here before us, and by the men and women who fought and campaigned for the establishment of Dail Eireann.
“Our democracy has remained strong through some of the gravest challenges of a turbulent century.
“We have continued to have free debate and free elections. We have never wavered in our commitment to the peaceful resolution of disputes.
“The most powerful thing about the mandate which each of us holds is that it is based on the support of our families, our supporters, in most cases our parties, and above all our communities.
“I could not be more thankful to all of those who have been at my side and have helped me to achieve the honour of being nominated to serve as taoiseach.”
Mr Martin then left the Dail to meet President Higgins at his official residence at Aras an Uachtarain in Dublin.
Micheal Martin with President Michael D Higgins (Maxwell Photography/PA)
There, he formally became the Irish premier after Mr Higgins signed the warrant of appointment and handed Mr Martin the Seal of the Taoiseach and the Seal of the Government.
The nomination was originally supposed to have taken place on Wednesday, but a dispute over speaking rights for independents affiliated with the incoming coalition led to the Dail being adjourned.
Mr Martin’s Fianna Fail emerged as the largest party after the Irish general election at the end of November.
It agreed to re-enter a coalition with Fine Gael, led by outgoing taoiseach Simon Harris.
The two parties combined were just short of a majority in the Dail and will be supported by several independent TDs (MPs) for the five-year government term after lengthy negotiations.
Efforts to nominate Mr Martin on Wednesday had to be abandoned over a disagreement on whether Government-affiliated TDs could be allocated opposition speaking time.
Simon Harris and Micheal Martin (Brian Lawless/PA)
The Dail reconvened at 11.40am on Thursday to proceed with the nomination of a taoiseach after extensive negotiations resulted in agreement that parliamentary rules needed to be reviewed.
Sinn Fein put party leader Mary Lou McDonald forward for the role, but she conceded in her speech that the bid would not be successful.
Mr Martin, 64, served as taoiseach in the last coalition government with Fine Gael and the Green Party.
That coalition introduced a “rotating taoiseach” mechanism which saw the top office swapped between the leaders of Fianna Fail and Fine Gael midway through the term.
The arrangement will be repeated, although on a three-to-two-year basis in favour of Fianna Fail in recognition of the party’s 10-seat lead over Fine Gael.
It continues a partnership which began in 2020 and set aside almost a century of animosity between the two parties forged from opposing sides of Ireland’s Civil War of the 1920s.
Mr Martin, from Cork, cites the moment Ireland became the first country to implement a workplace smoking ban in 2004 during his time as health minister as among his proudest political achievements.
Micheal Martin (Julien Behal/PA)
The son of an Irish international boxer, he has also held cabinet ministries for enterprise, foreign affairs, defence and education.
He has been the leader of Fianna Fail since 2011.
Mr Harris, the previous taoiseach and leader of Fine Gael, will take the deputy premier role of tanaiste.
Mr Martin will later nominate members of the next government.
The incoming cabinet will also travel to the State Reception Room of Aras an Uachtarain to receive their Seals of Office.
The final make-up of that cabinet will be closely watched with some departments expected to be reshaped as portfolios swap between Fine Gael and Fianna Fail.
Fianna Fail will hold most cabinet positions, with independents securing two “super junior” ministries with seats at the table during formation talks.
The independents-backed Government has already faced a number of rows around the make-up of the coalition.