A no-deal Brexit would be a failure that both the British and Irish governments would be responsible for, Boris Johnson has said.
The prime minister is in Dublin for his first face-to-face meeting with Taoiseach (Irish PM) Leo Varadkar since he entered Downing Street in July.
He said he believed a deal was still possible by the EU summit in October.
However Mr Varadkar said there was no such thing as a clean break between the UK and the EU.
Mr Johnson has ruled out asking the EU to delay the Brexit deadline of 31 October – but the Irish government said it would support another extension.
Ahead of the meeting, Mr Varadkar said he would be asking Boris Johnson how he plans to get a Brexit deal through Parliament when he does not have a majority in the House of Commons.
But Mr Johnson told reporters in Dublin that he was “absolutely undaunted” about what might happen in Parliament in the coming days.
He also said he had looked at the consequences of a no-deal Brexit, and “wanted to find a deal”.
“There are two tasks we simply have to do – we must restore Stormont and we must come out [of the EU] on 31 October, or else permanent damage will be done in the UK to trust in our democratic system,” he added.
Mr Varadkar said the Irish government “cannot and will not replace legal guarantee with a promise”.