UKIP leader Nigel Farage (pictured: Reuters) would take on David Cameron, Ed Miliband and Nick Clegg in a televised pre-election debate, under proposals from broadcasters.
The Tory and Labour leaders would also go head-to-head in another programme, according to the joint plans from the BBC, ITV, Sky News and Channel 4.
The announcement – which follows months of detailed negotiations over the format for debates next year – is said to reflect "changes in the political landscape".
Ukip came top in European elections in May, and secured its first elected Commons seat last week – while the Liberal Democrats have been languishing in the polls.
All parties have said they support more debates in principle, after the 2010 events dominated the campaign and drew significant audiences. But there have been disagreements about who should participate and how they will be staged.
The blueprint from the broadcasters would see former Newsnight host Jeremy Paxman chair a one-on-one contest between Mr Cameron and Mr Miliband for Sky News and Channel 4.
The Conservative, Labour and Liberal Democrat leaders would clash in a BBC debate presented by David Dimbleby.
And the trio will be joined by Mr Farage for an ITV programme chaired by Julie Etchingham.
The Ukip leader said the proposals recognised growing support for his party.
"The decision is better than it could have been. It does at least recognise the increasing popularity of Ukip," he said.
"However if the political landscape continues to change we would expect and ask for inclusion in a second debate."
The Liberal Democrats rejected the suggestion that they should be excluded from one debate.
"The Liberal Democrats have long argued that the debates last time round were of huge benefit to our democratic process and engaged millions of voters," a spokesman said.
"The Liberal Democrats therefore welcome the fact that the broadcasters are seeking to make progress to ensure that the debates happen again in 2015.
"The Liberal Democrats, like the Labour Party, have publicly said that we would be prepared to sign up to the same 3-3-3 system we had in 2010.
"We do not accept the proposal that the Liberal Democrats, as a party of government, should be prevented from defending our record in one of the TV debates.
"That is the case we will make strongly in the negotiations that will now take place and we urge the other parties to join us around the negotiating table without excuse or delay."
A statement from the broadcasters said the debates were "vital in engaging voters with the political process". The three encounters at the last election, each featuring the Tory, Labour and Lib Dem leaders, were watched by 22 million people.
"The broadcasters intend to transmit the leaders' debates live for all their extensive audiences, on air, online and on social media, which together have a mass reach amongst the British population," the statement said.
Farage was widely seen as emerging victorious from two debates with Clegg on the EU in the run-up to European elections earlier this year.
Last week Clegg accused Cameron of "foot-dragging" over encounters during the general election campaign.
"The Tories should come clean – if they want to run scared, they should say they don't want to do them, but not this endless ducking and weaving. I think people want the TV debates.
"The more people can see how the leaders measure up against each other, the better."