The British Prime Minister has said there was a "fantastic cause for optimism" after Stormont returned on Saturday, adding there was a "special opportunity" now for Northern Ireland's political leaders.
Rishi Sunak was speaking during a visit to Northern Ireland on Sunday evening.
Mr Sunak was in Lisburn where he met emergency responders and families who have been helped by Air Ambulance Northern Ireland.
Speaking to reporters, Mr Sunak said now that the Executive was back up and running, "it is right that people have their local politicians focusing on their priorities, starting with public services".
"There has not been devolved government up and running here for far too long. But now we do have it and they can start focusing on delivering for everyone," he said.
Asked out the £3.3 billion provided by the UK government to Stormont as part of the power-sharing return package, Mr Sunak said it was a "generous and fair settlement".
"And crucially, it is sustainable. It is about ensuring public finances in Northern Ireland are sustainable for the long term. That approach we have taken, I think will really benefit everyone here," he said.
Prime Minister Sunak is meeting Taoiseach Leo Varadkar in Belfast on Monday and will also meet the First and Deputy First Ministers at Stormont Castle.
It comes as the newly formed Executive meets for the first time on Monday.
Appointment 'demonstrates change across island' - O'Neill
Northern Ireland's First Minister Michelle O'Neill said her appointment "demonstrates the change that is happening across this island".
"The fact that this day is here, the day that was never supposed to come. That demonstrates change," she said.
Speaking on RTÉ's The Week in Politics, Ms O'Neill said she is so proud and will represent the "whole of society".
Ms O'Neill said she grew up in a state where discrimination was evident and things were "built in such a way" to keep her community down. She said thankfully that is in the past.
"We are now in a new era and looking towards the future. I am certainly looking forward to the future."
She reiterated her plans to reach out to all communities.
"That will be borne out in all my actions ... I think it is important we always reach out ... I am an Irish republican but I have pledged to work in tandem with ministers from all different parties, all different backgrounds."
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Sinn Féin leader Mary Lou McDonald said having a nationalist and republican occupying the office of First Minister in Northern Ireland is hugely and historically significant.
Speaking on RTÉ's This Week programme, she expressed the general relief that there is now a functioning Assembly in Northern Ireland because the day-to-day issues have to be tackled.
She said she sensed yesterday in Stormont not just the relief but also a great sense of purpose by everyone to make it work.
Border poll will be held during 'decade of opportunity' - O'Neill
Speaking on Sky News earlier, Ms O'Neill said Northern Ireland has begun a "decade of opportunity" during which it will hold a vote on unification with Ireland.
She said she expected a referendum on reunifying Ireland in the next 10 years.
"Yes. I believe we're in a decade of opportunity," she told Sky News when asked if she anticipated a border poll within that timeframe.
"There are so many things that are changing all the old norms, the nature of the state, the fact that a nationalist republican was never supposed to be first minister. This all speaks to that change."
Following two years of protracted negotiations, the DUP returned to power-sharing after this week agreeing a deal with London over post-Brexit trade rules it opposed.
As part of the agreement with the DUP, the UK government released a paper stating that it "sees no realistic prospect of a border poll leading to a united Ireland," citing recent polling.
"We believe that... Northern Ireland's future in the UK will be secure for decades to come and as such the conditions for a border poll are unlikely to be objectively met," it added.
Ms O'Neill said she disagrees with the assessment.
"I would absolutely contest what the British government have said in that document, insofar as my election to the post of first minister demonstrates the change that's happening on this island, and that's a good thing."
Ms McDonald said the conversation around unity is under way and thinks it needs to be acknowledged that there is a First Minister who is "a united Irelander".
She said preparation for constitutional transition and change needs to get under way and be "led by the Government in Dublin".
"The rule book is and remains the Good Friday Agreement in which this question will be adjudicated by means of referendums," added Ms McDonald.
Restoration of devolved government welcomed by leaders
Irish, British and US political leaders have welcomed the restoration of devolved government to Northern Ireland.
President Michael D Higgins congratulated Michelle O'Neill and Emma Little-Pengelly on being elected First and Deputy First Minister respectively.
The President said their obvious shared desire to work together offered the best of prospects for the institutions to serve all of the people and to meet their differing needs.
Taoiseach Leo Varadkar said he looked forward to an early meeting of the North-South Ministerial Council, to address important issues such as agriculture, food safety and tourism.
US President Joe Biden commended Northern Ireland's political leaders for taking the necessary steps to restore core institutions.
Northern Secretary Chris Heaton-Harris said he was "extremely confident" that the Stormont Executive would be "sustainable in the very long term".
