Tim Farron will tell the Liberal Democrats to ready themselves for a return to government in 2020 even if it means doing a deal with the Conservatives.
Mr Farron is to stress the importance of winning power and putting principle into practice in his first major address to the Liberal Democrat conference as party leader.
Voters punished the party at the election, reducing it to a rump of just eight MPs and dooming them to five years as a minor voice in the House of Commons.
The party hopes to take advantage of Jeremy Corbyn's election as Labour leader to win back centre left voters and rebuild, starting at the Scottish, Welsh, local and London elections in May.
And despite offering the Conservative-Liberal Democrat coalition marks of just "two out of 10" ahead of the general election, Mr Farron will insist: "I am proud of what we did in government and I am determined we will return to government."
Speaking to activists in Bournemouth, Mr Farron will add: "We will learn from the last five years but we will not repudiate the last five years.
"Five years where we learnt that power is tough but worth it."
Mr Farron will highlight success on boosting the personal tax allowance and gay marriage, as well as acknowledging his party made mistakes in office.
He will say: "I came into politics to change things, to make a difference, to make people's lives better. And to do that, you need the power to bring about change.
"There is nothing grubby or unprincipled about wanting to win. Nothing noble about defeat - losing sucks, losing robs you of your chance to make people's lives better.
"What's the point in being right if you never get to put your policies into action?"
The party has not changed its position on allowing electoral arithmetic to determine which parties are best placed to build a coalition. It is recognised a Tory-Lib Dem coalition is likely to be closer to a Commons majority than a Labour-Lib Dem arrangement in 2020 given how far behind Labour currently are.
Mr Farron, who served on the backbenches throughout the last coalition, replaced former deputy prime minister Nick Clegg as party leader in the wake of the devastating results.
But he will tell activists the party must stick to austere policies aimed at eliminating the structural deficit by 2017/18 - a position which demands spending cuts or tax rises.
Senior party sources accepted that on the economy, the Liberal Democrats are closer to the Tories than Mr Corbyn's Labour.
Mr Farron will say: "It's tough and I tell you frankly that it means that we won't be able to do all the things we might like to do in the short term.
"But not ending the deficit now means leaving the next generation to clear up our mess, and that's simply unfair.
"But what is equally unfair is to place the burden of ending that deficit wholly on the poorest and lowest paid - we must all play our part, based on our ability to pay."
Turning to the Chancellor, Mr Farron is set to add: "That, George, is what 'being all in it together' really means."
Mr Farron is due to spell out why the Lib Dems must be "the voice of small business".
He will also detail the party's planned opposition to Tory moves to extend the right to buy to housing associations.
Mr Farron will condemn the Government for being "unambitious" in postponing railway electrification in the north and suggest high speed broadband roll out is happening too slowly.
Drawing on the party's campaign in the EU referendum, Mr Farron will also say it is unambitious to "pull up the drawbridge" on Europe.