The UK will remain fully aligned to EU rules supporting Irish cross-border arrangements if no deal can be agreed, negotiators said.
Without an agreed solution the UK will maintain "full alignment" with EU internal market and Customs Union provisions which underpin North-South co-operation, the all-island economy and the protection of the 1998 Good Friday Peace Agreement which largely ended decades of Northern Ireland violence, the text disclosed.
The UK said it "remains committed" to protecting North-South co-operation and its guarantee of avoiding a hard border.
The joint report from EU and UK negotiators confirmed: "Any future arrangements must be compatible with these overarching requirements."
The UK's intention is to achieve this through the overall EU-UK relationship.
"Should this not be possible, the United Kingdom will propose specific solutions to address the unique circumstances of the island of Ireland.
"In the absence of agreed solutions, the United Kingdom will maintain full alignment with those rules of the internal market and the Customs Union which, now or in the future, support North-South cooperation, the all-island economy and the protection of the 1998 Agreement."
Under the Good Friday Agreement there is co-operation between Northern Ireland and the Republic on a wide range of areas including tourism, health, waterways and cross-border trade.
Many people cross the border every day for work and the mainly small and medium-sized enterprises on both sides of the frontier rely on on its openness to send goods back and forth.
The Good Friday Agreement enshrined many of the North-South co-operation measures in an international treaty between Ireland and the UK.
The breakthrough in the Brexit negotiations also contained concessions for the DUP.
It said: "In the absence of agreed solutions ... the United Kingdom will ensure that no new regulatory barriers develop between Northern Ireland and the rest of the United Kingdom, unless, consistent with the 1998 Agreement, the Northern Ireland Executive and Assembly agree that distinct arrangements are appropriate for Northern Ireland.
"In all circumstances, the United Kingdom will continue to ensure the same unfettered access for Northern Ireland's businesses to the whole of the United Kingdom internal market."