Cabinet Ministers have received their seals of office from President Michael D Higgins at Áras an Uachtaráin.
Earlier, TDs in the Dáil approved the new Cabinet nominations by Taoiseach Simon Harris by 87 to 68 votes.
Reshuffling Fine Gael Cabinet roles, Mr Harris nominated the junior minister, Peter Burke, as Minister for Enterprise, Trade and Employment, and the junior minister, Patrick O'Donovan, as Minister for Higher Education, Research, Innovation and Science.
Deputy Jennifer Carroll MacNeill will serve as Minister of State at the Department of the Taoiseach and the Department of Foreign Affairs, with special responsibility for EU Affairs and as Minister of State at the Department of Defence.
The remainder of the ministers of State will be made known tomorrow. TDs Alan Dillon, Emer Higgins and Colm Burke could be promoted to the junior ranks.
Speaking following his confirmation as Taoiseach, Mr Harris said that the Government was a "partnership Government" and paid tribute to Leo Varadkar as "a trailblazer".
He told the Dáil that he accepts his new role as Taoiseach "in a spirit of humility, ready for the challenge, and full of energy and determination about what can be achieved".
He said he believes that a Taoiseach "should work every day to realise the hopes, dreams and aspirations of all our people".
"Now is an opportune moment to build a new social contract, which renews our promise as a republic," he added.
Mr Harris told the Dáil: "I sincerely promise to be a Taoiseach for all. No matter your political persuasion.
"I will work with you and for you, and for the country that I know we all love. I will be a Taoiseach who will listen.
"The Irish story is a story of hope, a spirit of optimism sustained us in the darkest of days.
"And today, once again, we must ensure it lights our way forward.
"Let us not make the mistake of giving into pessimism and despair about our future."
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Humphreys proposed Harris as Taoiseach
Earlier, Minister for Social Protection and newly appointed deputy leader of Fine Gael Heather Humphreys had proposed Mr Harris as the next Taoiseach when the Dáil reconvened this morning after the Easter break.
She recalled the first time she met Mr Harris in the Dáil in 2011 and thinking the "young lad" was on a school tour or work experience.
Moments later she saw him make his first contribution in nominating Enda Kenny as Taoiseach.
"It took me a few weeks to make my maiden speech, he did it on day one, and I think anybody who heard him that day knew from the start he would go far," she said.
She described Mr Harris as having "endless amounts of energy", adding he was someone who "cares deeply about improving services for families".
Ms Humphreys said it was a "great honour" to propose Mr Harris as Taoiseach.
Minister of State Peter Burke seconded the nomination of Mr Harris, saying he would lead the coalition with a "renewed energy, with compassion, bringing it right back to the core of politics".
"I always knew he would be Taoiseach one day. This has perhaps come a little bit sooner than he might have planned or expected. But I know he will rise to the occasion.
"He has empathy, energy, experience, campaigning skills and political antenna to take us forward and I look forward to voting for him and the new Cabinet in the house later today."
Additional reporting: Micheál Lehane, PA
