Andy Burnham has vowed to involve Jeremy Corbyn in his team "from the outset" if he becomes the next Labour leader.
In a speech littered with references to Mr Corbyn, the shadow health secretary said he would unite Labour and help rebuild its "emotional bond" with voters.
Mr Burnham told supporters there was common ground between himself and frontrunner Mr Corbyn and admitted the left-winger had brought "real energy" to the race.
Mr Corbyn later said: "We welcome Andy's inclusive tone towards our campaign and the view is mutual - if we win we would involve Andy in our team if he was willing. From day one, whoever wins must pull the party together."
Mr Burnham also warned Labour risked becoming a protest party if it chose the wrong leader.
In recent days, former Labour leaders and Prime Ministers Tony Blair and Gordon Brown have suggested the party could become a protest party if Mr Corbyn wins the leadership contest.
Backbencher Mr Corbyn has emerged as the surprise frontrunner to take control of the party on September 12.
Today Mr Burnham told supporters in Manchester: "As this race has developed one thing has become very, very clear: Our party wants change, real change.
"What kind of change do we want? Is it change that has a reasonable prospect of uniting us or is it change that might push us apart. Is it change that will restore our prospects as a party of government or will it leave us as a party of protest? That is what this race has boiled down to.
"Coming out of this contest, there is a real risk of division within our ranks and that is why I am presenting my vision today as the only one that can unite our party."
Mr Burnham said Labour had "drifted away" from people and that the future of the party was "hanging in the balance".
Jeremy has brought real energy to this race. I want to capture that and would involve Jeremy in my team from the outset.
He promised to embrace the ideas of other leadership candidates Liz Kendall, Yvette Cooper and Mr Corbyn.
He said on issues such as housing and railways, he and Mr Corbyn had similar opinions.
"Jeremy has brought real energy to this race," said Mr Burnham.
"I want to capture that and would involve Jeremy in my team from the outset.
"I want the people who are drawn to his campaign, particularly young people, to help us rebuild our party from the bottom up, to re-energise it, make it the people's party once again."
Mr Burnham said Labour should fight the 2020 general election on a pledge to allow everyone access to "a decent and affordable home" to rent or own.
Ballot papers for the vote are due to begin arriving today and must be returned by September 10. The result will be announced on September 12.