Ireland's Leo Varadkar on Saturday took over as prime minister for the second time, a handover of power in line with a coalition deal struck in 2020.
Mr Varadkar replaced Micheal Martin as Taoiseach (premier) in a rotation between his Fine Gael and Martin's Fianna Fail parties.
The centre-right parties, the two main political partners in a three-party governing coalition, were forged from opposing sides in the Irish Civil War in the early 20th century.
They agreed to the rotating premiership as part of a coalition with Ireland's Greens following 2020 elections.
Mr Varadkar, a former doctor who is the son of an Indian immigrant, is stepping up from deputy premier. Even in his second stint in the role, at 43 he is still one of Ireland's youngest-ever leaders.
Speaking at a special sitting of the Irish parliament in Dublin, Mr Varadkar paid tribute to his predecessor Mr Martin, who he said had provided "reassurance and hope in difficult times".
He added: "I accept this nomination with humility and resolve and a burning desire... to provide new hope and new opportunities for all our citizens."
Mr Varadkar gained the support of 87 members of parliament in a vote on Saturday, while 62 voted against.
After the result, UK Prime Minister Rishi Sunak tweeted his congratulations to Mr Varadkar.
The 1998 Good Friday agreement of 1998 ended three decades of sectarian conflict in Northern Ireland that left more than 3,500 dead.
In a video posted on social media, Mr Martin earlier said it had been "the honour of a lifetime to serve" as Taoiseach.
Mr Varadkar was born in Dublin to an Irish mother who worked as a nurse and an Indian immigrant father who was a qualified doctor.
After gaining a medical degree from Trinity College Dublin, he went into general practice but stayed involved in politics, and in 2007 secured election for Fine Gael in Dublin West.
His tenure as Taoiseach was overshadowed by Brexit and the pandemic, during which he re-registered as a doctor and returned to work once a week while continuing to lead the country.