Jeremy Corbyn is to rally his supporters with a call for a new wave of grassroots activism to propel Labour to victory at the next general election.
Speaking at the public launch of his campaign to retain the party leadership in Manchester, he will tell activists "victories are not won in Parliament alone".
While he will acknowledge that Labour has "a mountain to climb" if it is to regain power in the general election, he will say that campaigning as a "social movement" will be the key victory.
"We are a social movement and we will win the next general election only as a social movement," he is expected to say.
"Some people don't get this yet. They think a movement is something instead of parliamentary politics. It's not. It's what will make a Labour government possible.
"We have lost the last two general elections. We cannot carry on as before. No one underestimates the scale of the task in front of us. We have a mountain to climb to win a general election and that's why we have to change how we do things."
Mr Corbyn, who is facing a challenge from former shadow work and pensions secretary Owen Smith after Labour MPs overwhelmingly backed a motion of no confidence in him, will aim his message directly at the activists who swept him to the leadership in last year's election.
"Victories are not won in Parliament alone. They are won because of public outrage. That outrage is being organised by you - party members, trade unionists - and it is only when we come together and campaign we win," he will tell them.
"This party is changing. Politics is changing - and it needed to. You are that change, you are the ones who will change politics and I want to make sure that you are empowered to do that.
"And then together we can oust this Tory Government and start building the fairer decent society we all want."
Amid complaints that critics of Mr Corbyn - particularly women - have been subjected to bullying and abuse, he will say there is no place in the party for intimidation and - in a comment at the MPs seeking to oust him - no place for "coups".
"We have to be disciplined," he will say. "I know some people are angry at the actions of some MPs but where we have disagreement in the Labour Party we settle it through democratic means - not coups, not intimidation, and not abuse."
Mr Corbyn's comments come after 28 women Labour MPs wrote to him in a letter organised by backbencher Paula Sherriff complaining at his "inadequate" response to the abuse.
"Rape threats, death threats, smashed cars and bricks through windows are disgusting and totally unacceptable in any situation," they wrote.
"This is acknowledged by all factions, yet the simple words of condemnation offered in response are inadequate. We expect swift and tangible action against those who commit such acts."
However one of Mr Corbyn's key allies, Unite trade union boss Len McCluskey, accused critics of exaggerating the abuse which he suggested was being orchestrated by the security services to discredit the Labour leader.
He pointed to the recent disclosure that an official in the old Transport and General Worker's Union in the 1970s had been an "MI5 informant".
"Do people believe for one second that the security forces are not involved in dark practices? Anybody who thinks that that isn't happening doesn't live in the same world that I live in.
Do you think that there's not all kinds of right-wingers who are not secretly able to disguise themselves and stir up trouble? I find it amazing if people think that isn't happening," he told The Guardian.