Leo Varadkar has regained the post of Taoiseach (Irish Prime Minister) under the agreement that underpins the coalition government.
The Fine Gael leader, who had been Tanaiste (Deputy Prime Minister) for two years, swapped roles with Fianna Fail leader Micheal Martin.
Mr Varadkar, 43, was nominated at a special sitting of the Irish Parliament before traveling to meet the president.
He told the House that the coalition was born “in a spirit of unity” during the pandemic and said he intended for it to continue.
“Providing hope and housing, economic opportunity and a healthy start for all” would be its mission, he added.
Leo Varadkar made history in 2017, becoming Ireland’s youngest Prime Minister and its first gay Taoiseach.
The son of an Indian doctor and an Irish nurse, he and Rishi Sunak share a similar heritage and politics.
Aoife Moore, the Sunday Times’ political correspondent in Ireland, said: “Leo Varadkar is the first gay Taoiseach we’ve ever had and the first minority Taoiseach we’ve ever had, Rishi Sunak the first minority prime minister…so this is a new start.”
“Rishi Sunak has already signaled that he wants to get a Brexit deal done…and both men are going to go there with that in mind, that they want everything sorted out,” she added.
But sorting it out won’t be easy when Unionists hold him personally responsible for the Brexit border in the Irish Sea.
During the negotiations, Leo Varadkar warned the EU that a hard border between North and South could lead to IRA violence.
In loyalist areas, they marked his return as Taoiseach by erecting posters threatening renewed loyalist violence instead.
Billy Hutchinson, a former loyalist prisoner and now leader of the small Progressive Unionist Party, said: “Whenever someone has a dislike for someone, the anger comes first and that’s what happened.
“You may have an argument with your neighbors but you have to resolve it.
“From that perspective, if he really wants the Republic of Ireland to work then he has to make sure he has friendly neighbours,” he added.
Leo Varadkar has been embroiled in controversy and a police investigation over his leaked GP report and isn’t as popular in the polls as he used to be.
A video of him in a Dublin nightclub, posted online two weeks ago, has sparked questions about privacy laws but also about his own judgement.
But he hopes to have at least two years to turn things around before the next general election.