Labour with Owen Smith as leader will push to give Britain a second referendum on European Union membership after a deal is struck on the terms of membership.
The leadership candidate said many Leave voters now regret their decision and are angry after being "clearly misled" by the Brexit campaign.
He insisted Labour should be committing to a second referendum, or at least a general election, once the nature of Brexit is finalised.
The former shadow work and pensions secretary told the Guardian the public will want to see the deal, adding: "And then we should give them another chance.
"That does mean a second referendum or a general election when the terms are clear. The Labour government should be committing to that."
He went on: "I think there are many people out there who voted in good faith for Brexit and who felt they were doing the right thing for their families and their communities and I respect them for taking that decision," he said.
"But I think a lot of people I know are now saying to themselves, 'It wasn't the right decision.' A lot of people are angry that they were quite clearly misled by the Brexit campaign."
Mr Smith, who joined the race to challenge Jeremy Corbyn for the party leadership on Wednesday, said either he or fellow challenger Angela Eagle should stand aside, depending on support, to give a unity candidate a free run at the leader.
Mr Corbyn won a vote among the party's ruling National Executive Committee to stand without the nominations of 51 MPs and MEPs and has strong support among the membership who will now vote on the leadership.
"Ideally, we would have one candidate, and the clarity of that one candidate versus Jeremy Corbyn," he said.
Ms Eagle however indicated that she may be willing to run in a three-way battle against both Mr Smith and Mr Corbyn, telling a central London event: "I will leave Owen to do this own thing, I'll do my own thing."
She said there should be no legal challenge to the NEC's decision but warned that Labour risks electoral wipeout in the north at the hands of Ukip, similar to that it has suffered in Scotland if Mr Corbyn remains leader.
The former shadow business secretary also lifted the lid on working in Mr Corbyn's shadow cabinet, complaining of "parallel organisations", "constant cancelled meetings" and a leader "pushing away" MPs.
Ms Eagle said: "There were many things that didn't work, I won't go into great detail here - parallel organisations, reading about the brief that you are meant to be representing in the newspapers because somebody has written a speech without talking to you about it, constant cancelled meetings with (shadow chancellor) John McDonnell, no liaison at all.
"And finally, an inability that Jeremy has to have his parliamentary party convince him of anything - no reaching out, a pushing away.
"And then in the end on the doorstep, just not resonating with Labour voters, let alone wider voters."