Nick Clegg would take the Liberal Democrats into a coalition after the next election which would put Ed Miliband in Number 10, he said on Saturday.
The Deputy Prime Minister suggested his party would do its "duty" by working with Labour in the same way it was now in partnership with the Conservatives if voters failed to return an overall victor in 2015.
It comes after Business Secretary Vince Cable indicated he would be open to taking over leadership of the party, which has seen its popularity plummet since going into government with the Tories.
Clegg said he hoped that by 2015 the public would see the Lib Dems had "created a better economy and a fairer society".
"If the British people, like they did last time, say no-one has won, then I'll be open to working with other parties," he told The People.
Asked if he could do business with Miliband, he replied: "Yes".
He added: "If the British people said that was the only combination which could work would be those two parties, in the same way as after the last election the only combination which could work was Conservatives and Liberal Democrats, it would be obvious that Liberal Democrats would need to do their duty."
The Lib Dems have struggled to retain support since signing up to the power-sharing deal in May 2010, with some voters uneasy about their partnership with the Tories.
A ComRes poll out on Saturday for the Sunday Mirror and Independent on Sunday put the party's popularity at just 10 points.
There was more bad news for the current coalition, with the same survey showing that nearly half of Britain's voters believe Chancellor George Osborne should be ousted.
Cable, a former Labour Party member, did not stand in the last Lib Dem leadership contest, believing his age - now 69 - would go against him after previous leader Sir Menzies Campbell was often dismissed as being too old.
Asked if he would put himself forward in the future, he told the Financial Times Weekend Magazine: "I wouldn't exclude it."
He added: "The worship of youth has diminished - perhaps generally - in recent years."