Johnson said he would ask lawmakers to vote Monday on a motion calling for an early election.
Johnson has been mulling his next move since Tuesday, when lawmakers blocked his attempt to fast-track an EU divorce bill through Parliament in a matter of days.
Lawmakers said they needed more time to scrutinize the legislation, making it all but impossible for Britain to leave the EU on the scheduled date of Oct. 31 with a deal.
The British government has been awaiting the EU's decision on whether to postpone the U.K.'s departure to prevent a chaotic no-deal exit. The request for a delay until Jan. 31 was ordered by Britain's Parliament to avert the economic damage that could come from a no-deal exit.
Though the EU has not given its answer, Johnson said it looked like the EU would grant the extension — and with it kill off Johnson's oft-repeated promise that Britain will leave the EU at the end of this month.
"I'm afraid it looks as though our EU friends are going to respond to Parliament's request by having an extension, which I really don't want at all," Johnson said.
Britain's next scheduled election is in 2022. If Johnson wants an early election, he needs to win a vote in Parliament by a two-thirds majority, or lose a no-confidence vote, which so far opposition parties have refused to call.
The main opposition Labour Party has said it would "support a general election when the threat of a no-deal crash-out is off the table."
European Council President Donald Tusk has recommended that the other 27 EU nations grant Britain a delay, yet many of the bloc's members are weary and frustrated at Britain's interminable Brexit melodrama. But they also want to avoid the economic pain that would come to both sides from a sudden and disruptive British exit.
So they are likely to agree, although politicians in France say President Emmanuel Macron is pushing for a shorter extension than the three months that Britain has asked for.
Johnson has vowed that, sooner or later, the UK will leave the EU on the terms of the deal he negotiated with the bloc.
He said the Dec. 12 election date would give lawmakers more time to scrutinize his bill, because Parliament would be in session until the formal campaign started on Nov. 6.
"So, the way to get this done, the way to get Brexit done, is, I think, to be reasonable with Parliament and say if they genuinely want more time to study this excellent deal they can have it, but they have to agree to a general election on Dec. 12," Johnson said.
Meanwhile, U.K. police and politicians have sounded alarms about what could happen in Northern Ireland under Johnson's proposed Brexit deal, with the region's police chief warning that a badly handled divorce from the European Union could bring violence back onto the streets.
Police have long warned that if Britain's departure from the EU imposes a hard border between the U.K.'s Northern Ireland and EU member Ireland, that could embolden Irish Republican Army splinter groups who are opposed to Northern Ireland's peace process and power-sharing government.
Police Service of Northern Ireland Chief Constable Simon Byrne told the BBC on Wednesday there also was potential for unrest among Northern Ireland's pro-British loyalist community. He said, depending on how Brexit unfolded, there could be "a lot of emotion in loyalist communities and the potential for civil disorder."
"There are a small number of people in both the loyalist and nationalist communities that are motivated by their own ideology and that have the potential to bring violence back onto the streets," he said.
The all-but invisible Irish border now underpins both the regional economy and the peace process that ended decades of violence in Northern Ireland.
The Brexit divorce deal struck last week between Johnson and the 27 other European Union countries contains measures to keep the Irish border open. But the plan has been condemned by Northern Ireland's Democratic Unionist Party, an ally of Johnson's Conservatives. The DUP says the agreement's proposal to keep Northern Ireland in line with EU goods and customs regulations would impose new checks and friction between Northern Ireland and the rest of the U.K.
Johnson's Conservative government acknowledges that "administrative procedures including a declaration will be required" on goods going from Britain to Northern Ireland after Brexit, but it says they would be minimal.
DUP lawmaker Nigel Dodds warned Thursday that the British government risked undermining "the political institutions and political stability in Northern Ireland by what you are doing to the unionist community."
"Please wake up and realize what is happening here," he told the House of Commons. "We need to get our heads together here and look at a way forward that can solve this problem. Don't plow ahead regardless, I urge you."