A confidence and supply deal between the Tories and the DUP is expected to be announced in the next couple of hours, the BBC has learned.
Pictures from inside Downing Street showed a deal being signed by the DUP’s Sir Jeffrey Donaldson and Gavin Williamson of the Conservative Party.
Theresa May is seeking the backing of the DUP’s 10 MPs after losing her majority in the general election.
Both sides have been in talks since the poll on 8 June.
Details of the agreement between the two parties are expected to be made public within hours.
Earlier, the leader of the Democratic Unionist Party (DUP) said a deal to support a minority Conservative government was “close”.
Writing in the Belfast Telegraph, Arlene Foster said: “I believe we are close to concluding an appropriate agreement with the Conservative Party to support a minority government on a confidence and supply basis.”
She added that “progress has been slow but we continue to work through the issues”.
Separately, Mrs Foster told Sky News that agreement between the DUP and Conservatives at Westminster could bring parties in Northern Ireland closer to a power-sharing deal.
The Northern Ireland parties have until 29 June to find agreement over restoring the devolved government.
The parties have been warned that if they cannot reach agreement then direct rule could follow.
Analysis: Enda McClafferty, BBC News NI political correspondent
The big question will be how much will Northern Ireland receive. There was some speculation last week it was £2bn, others have said it will be around £750m or £800m.
The figure will also be scrutinised in Scotland and Wales, because if they feel Northern Ireland is being put in a favourable position they will make a lot of noise towards Theresa May and her government.
However, Arlene Foster knows whatever bag of goodies they get from Westminster can only be cashed in if there is a Northern Ireland Executive up and running.
The official deadline for a deal at Stormont is 16:00 BST on Thursday, but Sinn Féin say the government has warned that the Queen’s Speech vote on Wednesday means the deadline is effectively Tuesday.
So Arlene Foster will return to Belfast to face extensive negotiations on all sides.
Parties have raised concerns that the ongoing DUP-Tory talks are undermining the negotiations on restoring devolution at Stormont.
However, Mrs Foster told Sky News: “We’re back in London again and my hope is that we will be able to finalise a deal between ourselves and the Conservative Party.
“I think that this agreement will bring the prospects of doing at deal at Stormont closer because this will have a positive impact in relation to Northern Ireland.
“I very much hope that this week we will be able to conclude on two agreements.”
Northern Ireland has been without a power-sharing executive since March and without a first and deputy first minister since January.
The institutions collapsed amid a bitter row between the DUP and Sinn Féin about a botched green energy scheme.
The late deputy first minister, Martin McGuinness, stood down, in a move that triggered a snap election.