The DUP has backed a deal to support the minority Conservative government in exchange for £1bn of additional funding, according to reports.
After talks at No 10 between Theresa May and DUP leader Arlene Foster, the pair hailed the agreement between the two parties.
Mrs Foster said she was "delighted" an arrangement had been agreed.
The Prime Minister said the DUP and the Tories "share many values" and the agreement was "a very good one".
The agreement was signed by Tory chief whip Gavin Williamson and the DUP's Sir Jeffrey Donaldson while Mrs May and Mrs Foster, along with Damian Green and Nigel Dodds, watched on.
Speaking in No 10, Mrs May said: "As we set out at the beginning of the talks, we share many values in terms of wanting to see prosperity across the UK, the value of the union, the important bond between the different parts of the United Kingdom.
"We very much want to see that protected and enhanced and we also share the desire to ensure a strong government, able to put through its programme and provide for issues like the Brexit negotiations, but also national security issues.
"So the agreement we have come to is a very, very good one, and look forward to working with you."
Ms Foster confirmed that the Prime Minister had agreed to abandon plans to scrap the pensions triple lock and introduce means testing for winter fuel allowance.
She added that the UK Government has committed an additional £1bn of funding for Norther Ireland over the next two years, and granted the country greater flexibility in terms of how £500m already committed can be spent.
The announcement comes just days before a crucial vote on the Queen's Speech and the June 29 deadline to restore a power sharing executive to Stormont.
The DUP has agreed to support the Tory government in passing the Queen's Speech and the Budget - which is the remit of a traditional confidence and supply arrangement - as well as legislation relating to Brexit and national security.
It is understood that the deal will not require further money to be committed to Wales or Scotland under the Barnett consequential, which is likely to trigger a fierce backlash among Scottish and Welsh MPs.
It is also likely to raise questions about the timescale for the agreement, and the prospect of further financial demands from the DUP once the two-year funding offer is delivered.
Commenting on the deal, Lib Dem leader Tim Farron accused the Prime Minister of "throwing cash" at the DUP while British schools "are crumbling and our NHS is in crisis".
"The public will not be duped by this shoddy little deal. The nasty party is back, propped up by the DUP," he said.
"It would be better for the people of Northern Ireland for the DUP to buckle down and focus on the talks process to restore devolved Executive at Stormont, to bring the political stability that is needed for inward investment and growth, rather than demanding cash injections from the Treasury."
Ed Cox, director of the IPPR North think tank, stated that if the Government is "serious about creating inclusive growth" it must also ensure the English regions have the funding they need to unlock their potential.
"The government's Shared Prosperity Fund rightly recognises the need for growth across the UK, but this should be funded on the basis of a proper devolved settlement for England, rather than weak national government horse-trading – otherwise it will serve to broker less, rather than more, unity in the UK," he said.