Johnson was forced to abandon his promise to leave the European Union on October 31, after MPs demanded he ask for more time while they debate the divorce terms he struck with Brussels.
EU ambassadors will meet early Monday to discuss his request to delay Brexit until January 31, under a plan that would allow Britain to leave earlier if parliament ratifies the exit deal, Brussels sources said, AFP reported.
Member states have already accepted a delay in principle to avoid the risk of a disorderly divorce, but some, mainly France, question how long it should be.
Later Monday, Johnson will ask the House of Commons to vote on a snap election, which he wants to hold on December 12 -- after MPs have had time to ratify his Brexit deal.
However, he faces defeat, as with his two previous election calls. He needs the support of two-thirds of the 650 MPs, but does not have even a simple majority.
The Labor party dislikes Johnson's Brexit deal and says it will not back an election until his threat of leaving the EU with no deal at all is removed.
Senior Labor MP Diane Abbott told the BBC Sunday the party "is up for an election", but added: "We are waiting to see what the EU says."
More than three years after Britons voted 52-48 percent for Brexit in a 2016 referendum, the country and parliament remains deeply divided.
Johnson, a leader of the "Leave" campaign, took office in July vowing to take Britain out of the European Union on October 31 whatever happens.
But MPs rebelled against his threat to sever 46 years of ties without a deal and passed a law requiring him to seek a delay if they refused to accept his divorce terms.
Johnson reluctantly sent the letter to the EU asking for the required three-month delay last weekend.
Paris says there has to be a strong justification to grant what would be a third postponement of Brexit.
"We must not give more time based on a political fiction but on (the basis that there will be) elections or a second referendum," France's European Affairs Minister Amelie de Montchalin said Sunday.
If a delay is granted, Brussels is likely to demand Britain put forward a nominee to join the incoming cabinet of EU commissioners -- a move likely to cause controversy in London.
Johnson this weekend accused MPs of holding Britain "hostage" by refusing to back his deal or an election.
If his bid fails there could be yet be another election vote, after two smaller opposition parties backed the idea of a December poll -- but with conditions attached.
Johnson wants MPs to ratify his Brexit deal before holding an election, a tough but not impossible task.
But the Scottish National Party and the Liberal Democrats, who oppose Brexit, want to abandon the deal and instead hold an election on December 9.
They proposed legislating for the poll -- a process that would only require a simple majority of MPs and could begin as early as Tuesday -- if the government agrees.