Jeremy Corbyn will be automatically included on the ballot in Labour’s leadership contest, the party’s National Executive Committee has ruled.
Unions said party rules were clear that the incumbent must be allowed to stand, but his opponents said he needed the support of 51 MPs or MEPs.
Mr Corbyn said he was “delighted” with the result of the meeting.
His challenger, former shadow minister Angela Eagle, said she welcomed the contest and was “determined to win”.
The secret NEC vote went 18-14 in the Labour leader’s favour following hours of talks.
A Labour Party 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.”
Speaking outside the meeting, Mr Corbyn told a crowd of journalists and supporters: “So I’m on the ballot paper… and we will be campaigning on all the things that matter.
“The inequality and poverty that exists in this country, the need to end the privatisation of our National Health Service, the need to give real hope and opportunity to young people all across this country.
“That’s what Labour exists for. And that’s the campaigning work we will be doing the length and breadth of this country.”
“That will strengthen our party in order to defeat this Tory government and bring in a government that cares for the people.”
Shadow chancellor John McDonnell, a key ally of Mr Corbyn, said on Twitter: “Jeremy on the ballot. Democracy prevails. We will use leadership election to sign up even more members and prepare ground for general election.”
But the BBC’s political editor Laura Kuenssberg said it was highly likely that the Labour Party itself would challenge the decision in the courts.
Ms Eagle has said she is challenging Mr Corbyn because she can provide real leadership which he cannot.
Reacting to the vote on Tuesday night, she said: “I’m glad the NEC has come to a conclusion. I welcome the contest ahead and I am determined to win it.”