LONDON — Jeremy Corbyn, the socialist leader of the opposition Labour Party, announced Friday he will step down after election results showed the party not only failed to oust the ruling Conservatives but also lost a swath of formerly dependable seats.

Corbyn admitted it had been a "very disappointing" night as support crumbled in his party's former heartlands, with Labour wining just over 200 seats in the 650-seat British Parliament.

Prime Minister Boris Johnson's ruling Conservative Party won 365 seats in Thursday's election, which was dominated by the furious and polarizing debate over Brexit and not social issues like the public health system.

Looking like a big win for Boris in the U.K.! — Donald J. Trump (@realDonaldTrump) December 13, 2019

Facing his second General Election defeat, Corbyn announced he would call it a day as leader after being re-elected to his Islington North seat in London.

He said he would not lead the party into another election, but would stay on during a “process of reflection.”

Many Labour figures are calling on Corbyn to resign immediately as the party grapples with what looks set to be an overwhelming defeat. But Corbyn seemed determined to resist the pressure, accusing the media of attacking Labour and contributing to its poor result along with Brexit.

A lifelong socialist, Corbyn, 70, will be remembered for transforming the party from a progressive but center-left political force that won three elections under Tony Blair, to a radical left-wing party that called for major reforms in business and the economy.

While he is popular among the party faithful — membership swelled under him — he is unpopular with many of his colleagues in Parliament, and several high-profile anti-Brexit Labour figures either quit, joined the rival Liberal Democrats or began their own mini-party.

Corbyn had been a largely unknown lawmaker since 1983, representing the inner-London suburb of Islington North and championing human rights. He was fiercely opposed to the 2003 invasion of Iraq and was chairman of the Stop the War Coalition, an amalgam of left-wing groups that organized several high-profile marches.

Along with John McDonnell, the would-be finance minister, Corbyn was one of the few hard-left members of Parliament to have survived the party’s modernization into “New Labour” under Blair, which abandoned a longstanding pledge to ensure industry was owned by the state for the benefit of workers, where possible.

Labour’s 2019 manifesto, a list of ideas and policies that British parties publish before an election, provided the clearest version of Corbyn's political vision.

Utility companies, such as water, energy and transportation, were to all be brought into public ownership. Companies were to give away 10 percent of its shares to workers, who would receive an annual dividend and get a say on boardroom decisions. High-speed broadband was to be made available to all homes and businesses for free. University tuition fees were to be abolished.

Alastair Campbell, a former Blair adviser and a rival of the party's leader, said the crushing defeat showed that voters had rejected Corbyn and the party's economic vision.

"Labour has to face some hard truths — this was not just about Corbyn but the broader worldview and an economic plan that so many people did not believe," he tweeted.

After a disappointing election result in 2015 under the center-left leader Ed Miliband, Corbyn stood for the leadership against some well-known New Labour figures and unexpectedly won. The party rules had just been changed to allow ordinary party members — not just lawmakers — to vote on who should become leader, which helped Corbyn to a landslide 59 percent victory.

Driven by Momentum, a campaign group set up purely to support Corbyn which amassed 40,000 members, Corbyn soon grew a huge following online and at a series of rallies across the country.

“Oh, Jeremy Corbyn,” sung to the bass line of the White Stripes’ "Seven Nation Army," became a familiar soundtrack at events, including at the music festival Glastonbury, where Corbyn was a guest speaker on the main stage in 2017, in front of tens of thousands of people.

His star rose further still after a spirited personal performance in the 2017 election helped Labour increase its overall vote share by 9.5 percentage points compared to the previous election, winning an extra 30 seats in the process, although not enough to claim power.

Corbyn’s tenure has been blighted, however, by accusations of anti-Semitism among some of his most fervent supporters, often tied to florid conspiracy theories concerning the state of Israel or Jewish bankers.

A series of reports, including from the Jewish Labour Movement, accused the party of not dealing with anti-Semitism complaints fast enough, a charge Corbyn flatly denied.

The U.K.’s chief rabbi, Ephraim Mirvis, made the unprecedented step before the election of writing in a newspaper article that “the very soul of our nation is at stake.” Some 87 percent of British Jews considered Corbyn personally anti-Semitic, according to a poll for the Jewish Chronicle in March.

Other controversies include his links and alleged support for the IRA in the 1980s.

In a BBC radio interview he was asked five times by the Northern Irish radio presenter Stephen Nolan to condemn the violence carried about by the IRA — he refused to do so and repeatedly said he condemned “all bombing,” including the actions of the British army during "the Troubles."

Corbyn faced strong criticism for an equivocal stance on Brexit — before the election he declared himself neutral in any second referendum — while the Conservatives scooped up pro-Brexit voters and the Liberal Democrats captured the anti-Brexit vote.

However, the long list of promises did not translate to electoral support, particularly in traditional working-class Labour heartlands where there is a natural suspicion of radicalism.

It's not clear whether Labour will continue in Corbyn’s mold and try to win support yet again at the ballot box for such a transformative agenda at the next election, scheduled for 2024, or whether the defeat means that the rump of centrist lawmakers who openly resented his leadership could try to wrest back control of the party.