Corbyn's rise echoes that of another senior-citizen socialist who has come out of nowhere this year to rattle his party's centre-left establishment.
Like Corbyn, Senator Bernie Sanders has been waging a surprisingly effective insurgency in a campaign that was once thought to be unwinnable.
"If you're Bernie Sanders, you'll take some heart from this," said Tim Bale, a politics professor at Queen Mary University of London. "If you're Hillary Clinton, you'll be nervous."
While Sanders is still fighting uphill to outmanoeuvre Clinton for the Democratic nomination, Corbyn's once-quixotic-seeming campaign ended with a landslide win. Nearly 60 per cent of voters backed him over three more centrist rivals just four months after Labour suffered one of its worst defeats in national elections.
In a fiery victory speech, Corbyn vowed to combat society's "grotesque inequality" and make Britain a more humane country.
"We don't have to be unequal," Corbyn told a crowd of cheering supporters at a London conference centre. "It doesn't have to be unfair. Poverty isn't inevitable. Things can -- and they will -- change."
Corbyn, who is often photographed biking around his posh north London district, pledged to unify the Labour Party's polarised factions. He may be helped in that task by Tom Watson, who was elected as deputy leader and is seen as a possible bridge between leftists and centrists.
But within minutes of the results being announced, it was clear just how difficult it will be to hold Labour together. Half a dozen prominent Labour politicians announced they would not serve in Corbyn's shadow cabinet.
The Conservative Party also unleashed a stinging attack that previewed what will likely be a relentless drumbeat for as long as Corbyn remains leader of the opposition.
Defence Secretary Michael Fallon charged that Corbyn's win had made the Labour Party "a serious risk to our nation's security, our economy's security and your family's security".
Blair and a chorus of other Labour titans had previously warned that a Corbyn victory would condemn the party to a long walk through the political wilderness.
But Corbyn capitalised on a widespread grassroots backlash against the political establishment that has grown out of the wreckage of the Iraq war and the widening wealth gap since the GFC.
Although Corbyn has served in Parliament for more than three decades, he succeeded by portraying himself as a straight-talking outsider who is unafraid to challenge the powerful, even within his own party.
He has previously called for Britain to leave Nato, favours unilateral nuclear disarmament and champions the nationalisation of vast sectors of the economy, including the railways and the energy industries.
He has also said that he will apologise on behalf of Labour for the Iraq invasion and that Blair could face war-crimes charges.
In his first official act as leader, Corbyn gave an impassioned address to tens of thousands of demonstrators who thronged central London demanding that the Government allow in more refugees from Syria and other conflict zones. He then joined in for a rousing rendition of The Red Flag, a socialist anthem.
In the crowd, some Corbyn backers popped champagne and guzzled it in the streets as they waved signs reading "Tories out, Refugees In". Wherever Corbyn went he was greeted with a chorus of "Yes, we did!"
The party saw a surge of new supporters this summer, many of whom paid £3 ($7.33) for the chance to vote for the party's new leader.
The ease of joining led to accusations that Labour opponents were joining up just to vote for Corbyn, and thereby torpedo the party's chances of winning the next election. But Labour officials said that they believed the vote had been free and fair.
Corbyn did not focus on the 2020 campaign in his victory speech, and analysts say it's more than likely he'll face an internal leadership challenge before that vote.
The radical left has also been on the rise in countries such as Ireland and Spain, both of which hold elections in the coming months.
The emergence of the radical left as a key player in European politics comes at least several years after the far right began asserting itself. In Britain, the anti-immigration UK Independence Party had its best-ever result in May elections, proving that voters on both ends of the spectrum are looking for alternatives to the traditional power-brokers.
Right leaning papers focus on divisions
Britain's pro-Conservative newspapers have crowed that socialist Jeremy Corbyn's crushing leadership victory will condemn the Labour Party to the opposition for a long time, while leftist media hailed the win.
"Bye Bye Labour!" screamed a front-page headline in the Sunday Express and the Mail on Sunday published a picture of the new anti-austerity firebrand next to the words "Red and Buried".
"Death of New Labour", said the Sunday Telegraph, referring to controversial former Prime Minister Tony Blair's famous brand from the 1990s. "Labour isn't dead, Blairism is. Jeremy Corbyn finally killed it," the paper claimed in an editorial that said "boring Blairites" had been vanquished.
The Sunday Times also picked up on the splits in the party and those figures who have said they will not serve under his leadership, with the headline: "Corbyn sparks Labour civil war".
The Independent on Sunday referred to Corbyn's appeal in his victory speech to new young Labour supporters and returning members, with a headline saying: "Welcome to the party, welcome home".
Guardian columnist Rafael Behr called Corbyn's election an earthquake "off the political Richter scale", pointing to the role of young people not previously involved in politics. "Blairism is buried beneath the rubble and a different structural and cultural divide has been revealed," he wrote for the pro-Labour daily.
Labour leader
Who is Jeremy Corbyn?
Corbyn was born in 1949 to a middle-class family. His mother was a teacher and his father an engineer, and they reportedly met while campaigning on the Spanish civil war.
As a teenager, he became involved in causes such as the Campaign for Nuclear Disarmament, and both Corbyn and his elder brother joined the Young Socialists.
Corbyn did not finish his studies at the North London Polytechnic. He was elected to Haringey Council, a municipal authority in north London, in 1974 aged 25.
He served as a full-time trade union organiser before he entered the House of Commons as MP for London's Islington North in 1983 -- a seat he has held since.
What are his causes?
Corbyn has been a fixture at left-leaning demonstrations for decades.
In 1984, he was arrested outside the South African Embassy in London for protesting against apartheid. As a long-time nuclear disarmament campaigner, he opposes the renewal of Britain's Trident nuclear fleet. In 2001, he helped establish the Stop the War coalition to campaign against the war in Iraq -- and he remains the group's chair.
Corbyn is patron of the Palestine Solidarity Campaign and takes a keen interest in championing "the rights of the oppressed" around the world.
Any controversies?
The Daily Telegraph has repeatedly noted that in 1984 Corbyn invited Gerry Adams, long-time leader of the Irish nationalist Sinn Fein Party and reputedly a former Irish Republican Army commander, to the House of Commons days after a deadly IRA bombing in England.
More recently Corbyn faced a television grilling when an interviewer asked whether he called the militant groups Hamas and Hizbollah "friends". Corbyn replied that he used the word in a "collective way" and did not agree with the actions of the two groups. But he said he believed "you have to talk to people with whom you may profoundly disagree".
Corbyn has long been known as a Labour rebel - he has voted to defy party whips more than 500 times.
What are his policies?
Within Britain, Corbyn wants to scrap university tuition fees and introduce laws to bring railways into public control. He wants to abandon economic austerity in favour of printing money to build affordable homes and other infrastructure.
Corbyn has stressed the need for what he called "tax justice" - "those with the most, pay the most" - and argues for cracking down on tax avoidance and evasion by businesses and the wealthy.
Abroad, Corbyn believes Britain should consider pulling out of Nato, wants Britain to spend less on defence and is against air strikes in Syria.
- AFP, AP
