Britain will remain in the European Union until next year unless Parliament ratifies Boris Johnson's Brexit deal sooner, the remaining member states have agreed.
Following a meeting of ambassadors, European Council president Donald Tusk said the EU 27 would accept the UK's request for a Brexit "flextension" until January 31.
The Prime Minister has said in the past he would prefer to be "dead in a ditch" than miss the October 31 deadline.
Mr Tusk tweeted: "The EU27 has agreed that it will accept the UK's request for a #Brexit flextension until 31 January 2020.
"The decision is expected to be formalised through a written procedure."
The Prime Minister's election bid on Monday, to be made under the Fixed-Term Parliaments Act (FTPA), would require a two-thirds Commons majority - 434 MPs - to agree to an election on December 12.
The PM will likely fail to secure "super majority" support for a December election on Monday - but knows he will require 100 fewer MPs to grant the same request just 24 hours later.
Labour's lack of support for the proposal means it is likely to be defeated when voted upon on Monday evening
Mr Johnson has already had two requests for an election refused, but the Liberal Democrats and Scottish National Party have offered Mr Johnson a way out of the deadlock.
Lib Dem leader Jo Swinson and the SNP's Westminster leader Ian Blackford have put forward a tightly-drafted Bill that would grant an election on December 9 - three days earlier than the PM's suggested polling date - as long as the European Union grant an extension until January 31.
The draft law, currently scheduled for Tuesday's sitting, would require a simple majority of 320 MPs to support it in order to dissolve Parliament - 114 fewer than under the FTPA "super majority" rules.
With the SNP and Lib Dems supporting the initiative, the Bill is likely to pass even without Labour backing.
Downing Street indicated it could be willing to support the pro-Remain parties' proposals in a possible compromise offer.
A Number 10 source said if the Government's request for an election was lost, "we will look at all options to get Brexit done including ideas similar to that proposed by other opposition parties".