LONDON — The U.K. and European Union announced Thursday they had agreed to a new Brexit divorce deal, a key breakthrough ahead of the Oct. 31 deadline for Britain to leave the bloc.

However the deal must still be ratified by European leaders and lawmakers in the British Parliament.

Negotiators for the two sides had been locked in talks ahead of a critical summit in Brussels later this week.

The agreement, which looked unlikely just days ago, could break the deadlock that has paralyzed British politics since the country voted to leave the E.U. in a June 2016 referendum.

Jean-Claude Juncker, the E.U. Commission president, and U.K. Prime Minister Boris Johnson, confirmed the detail Thursday morning on Twitter.

Johnson has staked his leadership on a promise to leave the E.U. on the current Oct. 31 deadline with or without a deal.

But rebel lawmakers passed a law forcing him to seek an extension if a deal had not been agreed by next Saturday, in an effort to prevent a “no-deal Brexit” that could have devastating consequences for the country.

If he is to keep his promise Johnson must now secure the support of the House of Commons, which his ruling Conservative Party controls despite having a minority of lawmakers.

The prime minister will likely need convince some of his opponents that his Brexit plan is better than the alternatives: Keep delaying the process, risk crashing out of the union without a deal at all, or cancel Brexit altogether.

The government may hold a vote on the deal this Saturday, when it has proposed holding a rare parliamentary session, the first on a weekend since 1982.

Johnson has been dealt a series of defeats in Parliament and saw his efforts to shut it down in order to force through his hardline Brexit plans ruled unlawful by the U.K’s Supreme Court.

His predecessor Theresa May failed on three occasions to win support for a deal she had agreed with the E.U., leading her to resign earlier this year.