A defiant Jeremy Corbyn said Labour MPs will understand they have to come together after it was agreed to automatically include him on the ballot in the party's leadership contest.
The Opposition leader said he was "delighted" that the secret vote of the ruling National Executive Committee went in his favour after hours of discussions at the party's headquarters in central London.
But the ruling will come as a major blow to the majority of Labour's MPs who are desperate to overthrow the party leader.
As jubilant supporters cheered Corbyn, he told reporters: "I'm sure Labour MPs will understand that the party has to come together in order to present to the British people the options of a different and better way of doing things."
Corbyn said he hoped his opponents would not mount a legal challenge over the decision.
Pledging to campaign "on all the things that matter", he said anyone who had any disagreements should "come and talk about it".
But the offer will do little to appease furious MPs who have complained bitterly about the difficulties of trying to engage with their leadership team.
Corbyn said: "I have been elected, last year, 10 months ago today, with a very large mandate. I respect that mandate. It's a responsibility I'm carrying out.
"I would hope there isn't going to be a legal challenge. There's been a very long legal discussion this afternoon. There were very well-qualified lawyers on hand to advise, so I think we are fine."
Corbyn posed for selfies with supporters as he emerged from the tense negotiations that lasted more than six hours.
NEC members wrestled with legal advice over whether the leader would need to secure 51 nominations to make it onto the ballot after both sides insisted Labour's rulebook backed their case. The committee favoured his position by 18-14.
Without automatic inclusion in the race Corbyn would almost certainly have been unable to defend his position.
The result is a significant setback for Angela Eagle, who faces a major battle to overturn his overwhelming backing among party supporters.
A Labour spokesman said: "The NEC has agreed that as the incumbent, leader Jeremy Corbyn will go forward onto the ballot without requiring nominations from the Parliamentary Labour Party and the European Parliamentary Labour Party.
"All other leadership candidates will require nominations from 20% of the PLP and EPLP."
Transport union TSSA said "good sense" had prevailed at the meeting.
General secretary Manuel Cortes said: "I am glad to see cool heads and good sense have prevailed at today's Labour Party NEC and should there now be a leadership contest that Jeremy will indeed be allowed to be on the ballot in accordance with party rules.
"Let's face it, with the Tories united behind Theresa May and our NEC now united behind Jeremy Corbyn it would be better for our members, better for our party and most of all, better for our country, if all sides of the party now come together, agree that we have more in common than that which divides us and work together to deliver a united and effective opposition to Theresa May's Tory government.
"But if there is yet to be a leadership contest, let it be conducted in a comradely manner and we at the TSSA look forward to supporting Jeremy continue to develop and expose his positive programme for the next Labour government."