But in 2019, there is a growing consensus that Corbyn, who this year turned 70, cannot go on forever and that the party must prepare for a new era.
Crunch moments once distant on the horizon are now fast-approaching.
A resolution to Brexit edges closer, as Labour’s deputy Tom Watson and others pile pressure on Corbyn to pick a side. The snap general election could either weaken the party’s left or give it another shot in the arm. The Equality and Human Rights Commission will soon rule on whether Labour is institutionally anti-Semitic.
And all the while, the Conservative Party under Boris Johnson is shifting away from austerity to target Labour’s northern power base, where voters have long been flirting with the likes of Ukip and the Brexit Party.
So, who is jostling for position, how might they win and who could get Corbyn’s all-important endorsement?
Ask trade unionists, MPs and shadow ministers, and most will underline the credentials of well-known frontbenchers such as Keir Starmer, Angela Rayner, Rebecca Long-Bailey and Emily Thornberry.
But this summer has revealed the extent to which Laura Pidcock is favoured by powerful left-wing unions such as Len McCluskey’s Unite, and by Corbyn himself.
Despite being elected for the first time in 2017, the campaigning MP has rapidly risen through the ranks to shadow minister and was earlier this month quietly promoted to shadow secretary of state for workers’ rights.
Pidcock now attends meetings of Corbyn’s top team where she has been described by some as “Jeremy’s de-facto deputy” as Watson’s appearances thin out.
The move was not, it seems, communicated to MPs.
“I had absolutely no idea Laura would be attending shadow cabinet, none of us did,” said one shadow minister.
Workers’ rights is a coveted portfolio for any would-be Labour leader, given it offers the holder regular interaction with unions, whose support can deliver votes en masse.
Corbyn’s decision to promote Pidcock also sees her absorb a large chunk of the brief belonging to potential rival Long-Bailey, who is shadow business secretary.
It is not the first time Corbyn has publicly demonstrated his support for Pidcock.
He was at her side at the Durham Miners’ Gala in July, in front of an audience jam-packed with union and Labour party members, as was McCluskey.
One Labour insider said: “I do think Len has a lot of admiration for Laura. When she came off the stage at the gala after her speech, he made a beeline for her and told her how proud they all were of her.”
HuffPost UK has also learned that plans by the leaders’ office for a joint Pidcock-Corbyn speech at the Trade Union Congress conference in Brighton earlier this month were blocked by union officials.
“The TUC general council is in control of the conference business so it was blocked. It was seen as a borderline endorsement and we wanted the leader of the opposition to have his own slot,” said a union source.
Pidcock allies say she is seen as “charismatic” and “has ambition but is very, very cautious”. Though a sizeable chunk of rank and file members want her to challenge for the deputy leadership now, she recognises she lacks the backing of MPs.
“She isn’t stupid and she’s not going to be bumped into something before she is ready,” one said.
They added that while her team may be looking to the “longer term” that “politics can change very quickly”.
It comes as Momentum founder Jon Lansman on Friday night tabled an emergency motion to the party’s ruling National Executive Committee to abolish the deputy leader post.
The extraordinary motion looks set to be heard again on Saturday and in the unlikely event that Watson’s position survives, his days as deputy are clearly numbered and those with ambitions for the top job are refocusing their efforts.
“Laura isn’t really part of any gang and gets on with a lot of people who do not share her politics,” one insider told HuffPost UK. “She isn’t dogmatic. She sees the party as a family and regularly asks people like Harriet Harman for advice.”
Pidcock has positioned herself as a darling of the left, with headline-grabbing statements, including that she has “absolutely no intention of being friends with any Tories” and regards Boris Johnson’s party as “the enemy”.
Laura isn’t really part of any gang and gets on with a lot of people who do not share her politics. She isn’t dogmatic. She sees the party as a family and regularly asks people like Harriet Harman for advice.Labour source
And she has not shied away from criticising other MPs within her own party - so often the source of members’ frustration since the failed 2016 attempt to depose Corbyn - and, having devoted long interviews with the strongly pro-socialist outlet Skwawkbox, does not have a groundswell of support among the Parliamentary Labour Party (PLP).
MPs also voice concerns about the strength of Pidcock’s links to the far left and say they find her depiction of politics as a "class war" unappealing. Her chief-of-staff, Ben Sellers, is also a former member of Militant.
Policy achievements she can point to within her brief include sectoral collective bargaining and offering workers full employment rights from day-one, both of which will bolster her popularity with unions.
But the 32-year-old new mother risks being on the wrong side of the Brexit argument, given the vast majority of Labour’s members are pro-EU.
Pidcock is from the traditional left of Tony Benn and, though she backed Remain, has Eurosceptic leanings.
Her North West Durham constituency backed Leave by 55% to 45% and it is thought the MP will campaign for a Brexit deal in any second referendum.
“She has quite a similar personality to Jeremy,” one source said. “There will be times that they disagree but they respect each other and they really get along.”
Support for her among the trade union movement is not universal, however.
Blair called David Miliband his Wayne Rooney. The difference is that Laura Pidcock is nowhere near ready for leadership or deputy leadership.Trade union source
“There is nothing wrong with a leader having a good political relationship and wanting to elevate,” said one source. “Blair called David Miliband his Wayne Rooney. It isn’t new.
“The difference is that Laura Pidcock is nowhere near ready for leadership or deputy leadership. Nobody doubts her potential but she still has a lot to prove.
“She does not have the experience, the confidence or the credibility to take on the job and the idea that she would have that in a year or two doesn’t hold water.”
Much depends on timing and right now the terrain on which the next leadership battle will be fought is unclear.
Should Labour face defeat at the polls in autumn, it is expected Corbyn will set out a timetable for his exit.
HuffPost UK understands even some of his fiercest critics will insist he stays for at least six months, both to hold together the opposition under a new government - many feel Ed Miliband’s decision to immediately vacate the pitch handed David Cameron an early advantage - and to guard against a traumatised membership rushing to a decision.
“Those around Corbyn will also want to be confident that they have the next leader lined up,” said one insider.
Should Labour emerge victorious in a snap poll, shadow ministers insist Corbyn will have the option to serve a full term.
MPs on the right of the party, however, have said an attempt to oust the leader is “inevitable” should the EHRC find against Labour.
Significant also are the divisions opening up between Corbyn and his closest ally John McDonnell, who has recently clashed with him and McCluskey over whether the party should campaign for Remain in a second referendum
An early contest could mean the winner is whoever has the strongest pitch to stop Brexit, something which is likely to favour Starmer or Thornberry.
McDonnell, who is believed to have the backing of Momentum, publicly rules himself out of any race but frequently tops members’ polls on who should replace Corbyn.
However, the influential shadow chancellor seems likely to throw his weight behind Long-Bailey, who appears to have a broad coalition of support.
The solicitor, who holds a dual Treasury and business brief, is a Corbyn loyalist and has a base of support among Momentum activists in Greater Manchester.
She has some support among the right of the party too, who may be prepared to team up with Momentum to back a compromise candidate.
“Laura Pidcock is untested and untried,” said one MP linked to the centrist group Progress. “Rebecca Long-Bailey and Clive Lewis are more tested and established figures.”
Long-Bailey’s other fans in the shadow cabinet include Shami Chakrabarti and others close to McDonnell.
“The best game in town is RLB,” said one shadow frontbencher.
“Rebecca has always been told she is a candidate rather than thinking she is a candidate herself, and I think that type of person should lead.
“She is incredibly hard-working, has incredibly strong values and it certainly doesn’t hurt that she is from the north.”
Most agree the person to lead the so-called “party of equality” should be a woman, given it has failed to ever elect a female to the top job.
Should Starmer run on a “stop Brexit” ticket - he has visited numerous constituencies allegedly fundraising and campaigning in recent weeks - his gender will nonetheless be seen as a drawback.
“One thing that really needs to be said and said again is that we are the party of equality,” said one MP. “It would be very, very hard for us to justify to the public why our next leader is a man. Nobody in our movement should think they are that special.”
But he has powerful allies among moderate MPs, in Scotland and in the trade union movement. Given his prominence in the Brexit debate, it will be argued Starmer could boost the party’s credibility if it suffers a heavy election defeats to Lib Dems and Tories.
“He is articulate, he is knowledgeable and, despite his professional career, he comes from a very ordinary background: his mother was a nurse and his dad was a toolmaker,” said one union backer.
“I don’t know if you can ‘out-joke’ Boris Johnson but Keir has a distinctive style and could be a good contrast.”
Thornberry, who has been frozen out by Corbyn after being so vociferous in backing Remain after the party’s near-destruction at May’s Euro-elections, has direct experience of opposing Johnson.
As shadow foreign secretary, she landed numerous blows on the now-PM over his conduct as a minister and his handling of the Nazanin Zaghari-Ratcliffe case.
I can’t see where Emily’s base is other than liberal, Remainy London.Trade union source
Speculation about Thornberry’s future took hold when she began standing in for Corbyn at PMQs - a slot which has since been occupied by Long-Bailey.
With around 50% of Labour’s membership believed to be based in London, Thornberry has got closer to the People’s Vote campaign and is heavily targeting Remain activists.
Holding Corbyn’s neighbouring constituency, Thornberry would be the second Islington MP to lead the party and some fear she could leave them open to claims Labour has lost touch with its working class heartlands.
“I can’t see where Emily’s base is other than liberal, Remainy London. She will also never get past the England flag debacle and so many MPs would be wary about backing her for that reason,” said one senior union source.
Long-Bailey’s credentials have been bolstered by her climate change brief and her role in the cross-party Brexit talks, but critics say she has rarely demonstrated a desire to lead.
“She would only agree to be a candidate out of sense of duty to the left, if, say, [Momentum founder] Jon Lansman and Len [McCluskey] sat her down and asked her to run because there was no-one else,” said one Labour source.
Long-Bailey also shares a flat with another candidate for the top job: shadow education secretary Angela Rayner.
The pair both hold North West seats and were part of the 2015 intake.
“They are very close and obviously a lot of people will focus on that. They have stuck together through thick and thin and I challenge anyone to find animosity between them,” said one senior Labour source.
Rayner is of the soft left tradition associated with figures like Ed Miliband and Sadiq Khan and has a compelling personal story. Having left school at 16 with no qualifications to raise a family, she later qualified as a social care worker and entered the labour movement as a rep for Unison, one of the largest if less political trade unions.
While those close to Rayner insist she has no plan to run, McDonnell, Pidcock and others signing a conference motion for a debate on abolishing private schools underlines that she is still regarded as a threat and will face pressure from the hard-left.
Moderates, meanwhile, are considering their options. While many acknowledge a Blairite cannot win with the current membership, Jess Phillips, who marked herself out early as an opponent to Corbyn’s far-left rule, could be be dispatched as “wrecking ball” candidate if the options leave critics with no skin in the game.
Pre-election, most MPs are reluctant to criticise the leadership or set out a timetable for succession.
This weekend’s Labour conference in Brighton, where MPs have high-profile speaking slots on the main stage and at fringes, will doubtless see all of the candidates jostle for position.
Pidcock, who can also count party chairman Ian Lavery among her allies is due to appear more than almost every other shadow cabinet minister and often alongside the influential McCluskey.
“The next leadership election will come down to what question are we trying to answer after the general election,” said one Labour campaigner, who believes Pidcock must branch out if she hopes to build a broad base of support. “If it becomes who is the heir to Jeremy Corbyn, then Keir can’t win. If it becomes who can stop Brexit then of course Keir can win.
"We also may be facing a debate about who can bring us back to the centre.
“At the moment, Laura is a one-battleground candidate.”