Theresa May has set out her commitment to Northern Ireland after Brexit in a six-point statement, including an assurance there will be no hard Irish border.
Her key commitments to Northern Ireland follow the announcement the European Union and the UK had reached a deal in the first phase of Brexit talks.
The prime minister's six-point pledge set out the government's "steadfast support for the Belfast Agreement" and promised to "fully protect and maintain Northern Ireland's position within the single market of the United Kingdom."
The Irish border had been a critical sticking point in advancing talks after the prime minister was forced to pull out of a potential deal with the EU earlier this week after meeting resistance from Democratic Unionists.
The DUP would not accept any Brexit deal that "separates" Northern Ireland from the rest of the UK with a hard border.
During Prime Minister's Question Time on Wednesday, Mrs May pledged to protect the "constitutional integrity" of the UK in a bid to break a deadlock.
Mrs May said today's agreement delivers on the principle, which she and Irish prime minister Leo Varadkar committed themselves in talks on Thursday, that "there should be no barriers, either north/south or east/west".
The DUP gave a cautious welcome to the deal, saying "substantial progress" had been made but that much more work was still needed on managing the Irish border post-Brexit.
DUP leader Arlene Foster said her party worked with the government into the early hours of Friday to secure changes to the original text.
Mrs Foster said Northern Ireland would now leave the single market and customs union and insisted there would be no border down the Irish sea, dividing Northern Ireland from the rest of the UK.
In her statement, Mrs May said: "As a Prime Minister who hugely values Northern Ireland's position within our United Kingdom - and believes passionately that the United Kingdom is stronger and better together - I want to set out six key commitments to Northern Ireland, principles that have guided me in the negotiations with the EU.
"This Government will continue to govern in the interests of the whole community in Northern Ireland and uphold the Agreements that have underpinned the huge progress that has been made over the past two decades."
Theresa May's six commitments to Northern Ireland post Brexit
First, we will always uphold and support Northern Ireland's status as an integral part of the United Kingdom, consistent with the principle of consent. The Government I lead will never be neutral when it comes to expressing our support for the Union.
Second, we will fully protect and maintain Northern Ireland's position within the single market of the United Kingdom. This is by far the most important market for Northern Ireland's goods and services and you will continue to have full and unfettered access to it.
Third, there will be no new borders within the United Kingdom of Great Britain and Northern Ireland. In addition to no hard border between Northern Ireland and Ireland, we will maintain the Common Travel Area throughout these islands.
Fourth, the whole of the United Kingdom, including Northern Ireland, will leave the EU customs union and the EU single market. Nothing in the agreement I have reached alters that fundamental fact.
Fifth, we will uphold the commitments and safeguards set out in the Belfast Agreement regarding North-South Co-operation. This will continue to require cross-community support.
Sixth, the whole of the United Kingdom, including Northern Ireland, will no longer be subject to the jurisdiction of the European Court of Justice.