The agreement between Sunak and European Commission president Ursula von der Leyen follows months of discussions between the UK and EU over what was known as the Northern Ireland Protocol, a controversial trade agreement for the region that came into effect in 2021.
The protocol was designed to prevent a hard border between Northern Ireland and the Republic of Ireland – and any future Brexit agreements must do the same.
However, the protocol was unpopular with unionists in Northern Ireland, who felt that it put a de facto sea border between them and the rest of the UK.
Following their meeting, Sunak and von der Leyen announced a new deal known as the Windsor Framework had been agreed, ironing out many of the issues with the previous deal.
Speaking in the House of Commons on Monday, Sunak said: "This is fundamental, far-reaching change and it permanently removes the border in the Irish Sea."
Yahoo News UK breaks down what the new framework is and why it's important:
Read more: Will MPs vote on Sunak’s Brexit plan and can it be blocked? (The Telegraph, 3-min read)
What is the Windsor Framework?
The Windsor Framework is a new post-Brexit trading deal, designed to remove the need for checks on goods travelling between Northern Ireland and the rest of the UK.
In a press conference with von der Leyen on Monday, Sunak said the new plan "delivers smooth-flowing trade within the whole of the United Kingdom, protects Northern Ireland's place in our union and safeguards sovereignty for the people of Northern Ireland".
The previous Northern Ireland Protocol was agreed between the EU and UK to prevent a hard border between Ireland and Northern Ireland, and effectively established a sea border between the mainland and the island of Ireland.
The Windsor Framework sets out a two-tier customs system that sees goods remaining in the UK (heading to Northern Ireland) put in a 'green lane' that avoids customs checks, while subjecting goods bound for the Republic to the 'red lane' for customs.
Watch: Brexit: Rishi Sunak and Ursula von der Leyen hold a press conference on new deal
Under the previous system, there was a free-flow of goods between north and south, but there were trade barriers between Northern Ireland and the rest of the UK.
Furthermore, the protocol kept Northern Ireland in the EU single market for goods, and it therefore still had to follow some rules set by the EU.
All of this meant that the protocol was vehemently disliked by unionist parties, including the Democratic Unionist Party (DUP). They argued that the protocol effectively created a border between Northern Ireland and the rest of the UK – thereby making them second-class citizens compared to people in England, Scotland and Wales.
The new deal will also see UK-approved medicine available in Northern Ireland at the same time as the rest of the country, while a "Stormont brake" has been approved that allows elected politicians in Northern Ireland to make decisions on which EU goods laws apply to them.
Rishi Sunak to meet Ursula von der Leyen for talks (Evening Standard, 5-min read)
What's the problem with a land border?
A land border between Northern Ireland and the Republic would have undermined the Good Friday Agreement, which was signed in 1998 and is credited for maintaining peace in the region.
During the discussions around Brexit, it was agreed that preserving the Good Friday Agreement (also known as the Belfast Agreement) was key, and prompted widespread discussion about how best to manage trade in a post-Brexit Northern Ireland.
The Good Friday Agreement is a framework for peace following a turbulent period in Irish history known as The Troubles. The multi-party agreement laid out arrangements over power sharing and the rights of people in the Republic and Northern Ireland over identity and citizenship.
Putting a land border between Northern Ireland and the Republic was therefore seen as hugely incendiary, given the two spent decades bitterly fighting over whether the north should return to be part of a united Ireland or remain part of the UK.
For Rishi’s Northern Ireland deal to work, he must listen to the unionists (The Telegraph, 5-min read)
What about Boris Johnson?
While former prime minister Boris Johnson agreed in 2020 to the existing Northern Ireland Protocol, Sunak's new deal changes things.
The Windsor Framework puts a sea border between the UK and the Republic of Ireland, but not between the UK and Northern Ireland – effectively creating a "two-lane" border system.
This would see goods from the UK bound for the Republic subject to checks at the sea border but not goods bound for Northern Ireland.
Sunak has also secured a "Stormont lock" that would allow elected Northern Ireland officials to have some say – but not a veto – over which EU trade rules it follows in the future.
Johnson previously already suggested making a new deal on the Northern Ireland protocol would be a "great mistake", while his reaction to the deal will be watched closely by his allies and detractors as an indicator of how some backbenchers will take the news.
He has not yet made a statement on the new accord.
Read more: John Major warns Boris Johnson’s ‘neuralgic’ supporters must not sabotage Rishi Sunak’s Brexit deal (The Independent, 5-min read)
What is Article 16?
Article 16 is a safeguarding clause worked into the Brexit deal that allows the UK or EU to suspend any part of the deal that is causing “economic, societal or environmental difficulties that are liable to persist, or to diversion of trade”.
If the UK had triggered Article 16 over the Northern Ireland Protocol, the EU suggested it would have responded with legal action, as it does not believe the situation warrants such a move.
What is Article 16 and what happens if UK triggers it? (The Independent, 2-min read)
What does the DUP say?
There are fears Sunak has not done enough to secure the backing of the DUP, which insists Northern Ireland should not be subject to any EU involvement. The party is currently boycotting the devolved assembly in Stormont over the issue, which is putting further pressure on Sunak to find a way forward.
The prime minister's allies hope that the two-lane border system and greater say over which EU trade rules to follow will be enough to win over the unionists; however, it is hugely unlikely they will give the deal their backing today.
The DUP leader Sir Jeffrey Donaldson said on Monday that while “significant progress” has been made on the new deal, “there remain key issues of concern”.
In Parliament, Donaldson said the new deal "vindicated" the DUP over the Northern Ireland Protocol following a long campaign to scrap it.
Speaking on BBC Radio Ulster a day after the new deal was announced, Donaldson insisted his party was “absolutely not” divided on the framework and that they would "take as long as it takes" to review the deal.
“Let me be clear, our party officers, our assembly members, our members of parliament, and ultimately, our party executive, will determine the party’s approach on this issue,” he said.
“We will consult and we will take our time. We will talk to people. We will listen to what people are saying, they will articulate their views. Of course, there will be a diversity and a range of views.
“People will react in different ways. But the DUP will come to a collective decision on this agreement.”
DUP warns Rishi Sunak it will not ‘compromise’ on Brexit red lines (The Telegraph, 4-min read)
Other reactions to the framework
While the DUP is yet to release a comprehensive statement on the new deal, the business community in Northern Ireland has largely responded positively to the news
“It is our shared aspiration that this agreement will deliver a unique platform that unlocks economic growth and investment, but we will now need time and space to work through the technical detail with our members," the Northern Ireland Business Brexit Working Group said in a statement.
Sunak acknowledged on Monday that the new deal would take time for people to digest, but said the framework would "end the uncertainty and challenge for the people of Northern Ireland".
Londonderry Chamber president Selina Horshi said: “We are hopeful that this new agreement will further smooth trade for local businesses, iron out any of the problems for traders, and bolster our unique market position which guarantees this part of the world access to the European and British markets. However, above all, we are hopeful that this deal now paves the way for the full and speedy return of the Executive and Assembly at Stormont."
Meanwhile Northern Ireland minister Steve Baker sad the deal was a "triumph".
“I’m absolutely convinced that this restores, by any legitimate measure, Northern Ireland’s place in the union,” the Brexiteer told the BBC. “It’s great news. It’s an extraordinary achievement. It’s a terrific thing to have pulled off.”
However, other Brexit hardliners are yet to respond to the news, although it is thought that there will be little significant rebellion over the new deal.
Following Sunak's speech in the Commons on Monday, Labour leader Keir Starmer said his party would back the deal, which he said was in the national interest, although he added that it was "not perfect" and that there would "inevitably be trade-offs".
Read more: Tory Brexit hardliners mulling response to Sunak’s Northern Ireland deal (The Guardian, 3-min read)