Sir Keir Starmer has seen his reform of Labour's rulebook approved by the party's conference in Brighton despite another day of opponents continuing their fight against the changes.
In a vote at the Labour gathering in Brighton, Sir Keir's overhaul of how the party elects future leaders was passed by 53.67% to 46.33%.
But the victory for Sir Keir and his allies came only after they watered-down their initial plans and as a battle over the reforms continued to overshadow the opening two days of Labour's conference.
Under the reforms, leadership hopefuls will now have to secure the support of 20% of the party's MPs (up from the current 10%) before becoming an official candidate in a leadership contest.
And a "registered supporters" scheme, which allowed people to pay a one-off fee to vote in a Labour leadership election, has been scrapped.
Sir Keir's reforms have also made it harder for current Labour MPs to be de-selected, by raising the threshold for triggering a selection contest.
Despite having initially hoped for wider reforms, the changes Sir Keir did manage to get approved represent a move away from the system that saw Jeremy Corbyn twice successfully stand for Labour leader.
Critics have accused Sir Keir of overseeing an attempt to shut out Labour's membership and its left wing from future leadership elections, with allies of Mr Corbyn having urged conference attendees to reject the leader's plans prior to Sunday's vote.
In other votes on Sunday, Labour members also supported the introduction of a fully independent complaints process following a critical report by the Equalities and Human Rights Commission.
And other safeguarding and discipline measures were also approved.
Sir Keir said he was "delighted that these vital reforms have passed", adding: "They represent a major step forward in our efforts to face the public and win the next general election.
"This is a decisive and important day in the history of the Labour Party. I promised to tackle antisemitism in our party. We've now closed the door on a shameful chapter in our history.
"I want to acknowledge the courage of all the people who spoke up against it.
"As I promised when elected as leader, the Labour Party is now relentlessly focused on the concerns of the British people and offering them a credible, ambitious alternative to this government.
"This is a crucial step forward for party I lead and am determined to see in government. And in the coming days you'll hear us set out ideas on how we win the next election."
But, prior to Sunday's voting, Sir Keir was forced to sit and watch his party and trade union leaders argue over his planned reforms of Labour leadership contests in front of the conference's "Stronger Future Together" slogan.
Dave Ward, general secretary of the Communications Workers Union, claimed Sir Keir had tried to "bounce" trade unions into backing his reforms.
"I'm here to say to you from the CWU point of view we have not been consulted and I don't want it implied that we had been," he told the conference.
"Had we been consulted we would have made the point that we feel that we're being bounced.
"And even at this late stage Keir, I think you should reflect on whether or not this needs to come to this particular conference.
"I'd ask you to think about creating unity in the party, looking outwards and deferring the leadership election changes that you're bringing forward."
Matt Wrack, general secretary of the Fire Brigades Union, branded the reforms "undemocratic" and claimed they "reduce the rights of party members and of affiliates".
"They seem to privilege MPs, they seem to be for the few rather than for the many," he added.
"But the idea that this will convince voters is completely untenable and unconvincing.
"It seems to see our party members, and, indeed, our affiliates as the problem. This party relies on its members and its affiliated organisations."
Megan Clarke, of Warwick and Leamington Labour Party, wore a Jeremy Corbyn T-shirt as she claimed the changes would "limit the ability of the left of the party to lead us in the future".
She said: "This is not simply about left versus right. This is about increasing the power of MPs to choose our leader.
"This is about disrespecting the rights of hundreds of thousands of members and affiliate members."
However, Labour's national campaign coordinator Shabana Mahmood MP, rejected the suggestion that the reforms would limit the diversity of future leadership candidates.
"The Parliamentary Labour Party for the first time ever is over 50% women, and it's the most diverse it has ever been when it comes to black, Asian and ethnic minority members of parliament," she said.
"Look at my face, look at every female MP for the Labour Party, look at every single black, Asian and ethnic minority Labour MP.
"The idea that we stand quietly by and deliver you a future contest that is pale, male and stale, you're having a laugh."