Veteran left-winger Corbyn, 68, was the surprise winner in a contest that followed the resignation of centre-left leader Ed Miliband after disappointing results in the 2015 general election.
Corbyn's election reflected a victory for Labour's more idealistic left in a long-term struggle with pragmatic centrists, who insist that the party's electability is paramount.
He was buoyed by an influx of mostly young activists that swelled party membership, and by the backing of major trade unions.
But he was forced to join a contest to remain in power in July after a revolt against his leadership by the majority of Labour's 220 MPs, including the resignation of most of his shadow cabinet.
Corbyn has often looked like cannon fodder for Britain's mainly right-wing media, which - joined by May and her Cabinet - are portraying him as a bumbling political extremist in the general election campaign.
Many analysts, as well as some prominent Labour politicians, had forecast electoral meltdown followed by years in the political wilderness unless the party ditches Corbyn and finds a new leader who appeals more to the centre ground of British politics.
When Labour launched its election manifesto in mid-May, the London Evening Standard - edited by former Conservative chancellor George Osborne - published the front-page headline: "Comrade Corbyn flies the red flag," warning that "Labour targets Londoners with 48-billion-pound raid on the better off".
The right-wing Daily Mail, one of Britain's two most popular tabloids, led its story with the headline: "Corbyn's class-war manifesto".
Other critics, including some in his own party, mocked Corbyn's manifesto for tonight's election as a contender for the new "longest suicide note in history," echoing the epitaph given to former leader Michael Foot's left-wing Labour manifesto before a disastrous election in 1983.
Yet Corbyn has appeared composed in media interviews and at campaign events, sticking to his core message of bringing greater social justice and economic equality to a post-Brexit Britain.
His confidence was reflected in his decision to join a BBC debate just eight days before the election, despite his earlier insistence that he would do so only if May - who ruled out appearing in a debate - was also present.
Corbyn's change of mind could have been spurred by a series of more recent opinion polls that have put Labour no more than 12 points behind, with several suggesting it could have reduced the gap to the Conservatives to just a few points.
Despite the initial predictions of doom for Labour, in a time when many votes seem to bring surprises, some are wondering if there could yet be another one in store.
- DPA, AAP
