The legislation designed to force Boris Johnson to delay Brexit beyond October 31 in order to avoid no-deal has been passed by the House of Lords.
The European Union (Withdrawal) (No.6) Bill is now awaiting royal assent to become law.
It comes after Jeremy Corbyn and other opposition leaders agreed not to approve the PM’s plan to hold a snap general election before the EU summit on October 17.
Any extension to Article 50 would need to be signed off by EU leaders at the upcoming gathering.
Johnson has said he would rather “die in a ditch” before asking Brussels for another delay. But under the terms of the bill, the government would legally have no choice.
The PM’s demand for an election on his own terms has become increasingly unlikely.
Corbyn spoke with leaders of the main opposition parties on Friday to discuss their resistance to holding a vote before the prospect of a no-deal Brexit on October 31 is eliminated.
Labour, the Liberal Democrats, the SNPs and Plaid Cymru are all understood to be planning on voting against or abstaining from the Fixed-Term Parliament Act when it returns to the Commons on Monday.
Opposition leaders including the Lib Dems’ Jo Swinson, the SNP’s Ian Blackford and Plaid Cymru’s Liz Saville Roberts discussed tactics on Friday morning as Johnson returned to the campaign trail of the election he is yet to successfully trigger.
Labour said the leaders discussed efforts to prevent a “damaging” no-deal Brexit and to hold an election “once that is secured”.
SNP Westminster leader Blackford said he was “desperate for an election”, but it could not be until an extension to Article 50 was secured.
He told PA Media: “It’s not just about our own party interests, it’s about our collective national interests.
“So we are prepared to work with others to make sure we get the timing right, but the timing right on the basis of securing that extension to Article 50.”
But he did anticipate that an election would be successfully called “over the course of these weeks”.
A Lib Dem spokeswoman said: “The Liberal Democrat position for a while now is that we won’t vote for a general election until we have an extension agreed with the EU. I think the others are coming round to that.
“As a group we will all vote against or abstain on Monday.”
The development came a day after the PM suffered a torrid day in which his brother resigned from government while describing being torn between family and “the national interest”.
The PM has said he wants polling day to be October 15, but in order to call the snap election he needs a two-thirds majority in the Commons and opposition parties do not trust him to stick to that date.
They also have concerns about whether he will comply with the cross-party legislation due to be passed by the House of Lords on Friday which would require him to seek a delay to Brexit if there is not a deal in place by October 19.
Johnson used a rambling press conference on Thursday to say he would rather be “dead in a ditch” than ask for a further delay.
On Friday, during his visit to Scotland, he declined to rule out resigning if he fails to deliver Brexit on the current deadline.
“That is not a hypothesis I’m willing to contemplate. I want us to get this thing done,” Johnson said.
There were also further signs of unease within the Tory ranks about the uncompromising Brexit stance which saw Johnson boot 21 senior Conservatives - including former chancellors Ken Clarke and Philip Hammond - out of the party in the Commons by removing the whip.
Former defence secretary Sir Michael Fallon, who is standing down as Tory MP in Sevenoaks, said he hoped an appeal mechanism would be put in place for his former colleagues.
He added: “I also worry that it sends the wrong message to remainers - particularly in my party.”