Theresa May and Jeremy Corbyn have agreed to take part in a live TV debate on Brexit before MPs vote on the deal.
The prime minister said she was the only one with a plan for the UK's future - Labour said Mr Corbyn would "relish" the chance to challenge that.
Mrs May refused to take part in TV debates with Mr Corbyn in the run-up to last year's general election.
The SNP, Lib Dems, Plaid Cymru and Greens have demanded to be involved to ensure a range of views is reflected.
However, Mrs May has rejected calls for smaller political parties to join in, saying she and Labour leader Jeremy Corbyn represented almost 90% of MPs in the Commons between them.
Former foreign secretary Boris Johnson said Mrs May should be holding a debate with "someone who believes in Brexit", saying there was "no point" in the head-to-head with the Labour leader and that it offered a "false choice".
He wrote on Twitter: "Debates are great for democracy - but rather than widening discourse, this debate is narrowing it by offering a false choice between May's failing deal and Corbyn's vague proposals - neither of which are Brexit.
"There is no point having a debate with two people who voted Remain and deals that don't take back control."
Mrs May is beginning a two-week campaign to sell her Brexit deal to the public and MPs, before the vote in the House of Commons on 11 December.
A day after the suggestion was first mooted in the Daily Telegraph, she told the Sun the format of the debate would be "a matter for broadcasters to determine", but she was on board.
"I am going to be explaining why I think this deal is the right deal for the UK - and yes, I am ready to debate it with Jeremy Corbyn.
"Because I have got a plan. He hasn't got a plan."
BBC assistant political editor Norman Smith said no date had yet been chosen for the debate, but it's expected to happen a few days before the vote.
Liberal Democrat leader Sir Vince Cable demanded to be involved as well, because, as he put it, neither the Conservatives nor Labour had called for a new referendum on the deal. The Greens, too, said any debate must be cross-party and diverse.
In a tweet, Plaid Cymru leader Adam Price said: "I'm ready to make sure Wales's voice is heard in any TV debate."
Scottish First Minister Nicola Sturgeon tweeted that she would be "up for a full leaders' debate on the 'deal'".
UKIP also wants its leader Gerard Batten to be involved in the debate.
On Sunday, EU leaders approved the Withdrawal Agreement and Political Declaration on future relations, which Mrs May has negotiated.
Labour, the Lib Dems, the SNP, the DUP and many Tory MPs have said they will vote against it.