He achieved this, despite the repeated efforts by the "New Labour" or "Blairite" wing of his own party in Parliament to unseat him as leader, and their constant efforts, both in public and in private, to undermine him.
Imagine what he could have achieved if he had had a united party behind him and a fair go in the press!
So, what did he have going for him? What explains the unexpected (and admittedly comparative) success that he and Labour enjoyed?
What seems to have attracted voters is that he was willing to talk to them, not as a politician but in human terms - in marked contrast to Theresa May, who was so robotic that she attracted the nickname "Maybot". Corbyn, by contrast, attracted huge crowds, and seems to have particularly enthused young voters.
What did he talk to them about? He talked to them about what a good and decent society looks like, about how its members should treat each other, about government's responsibility to ensure that no one gets left behind and that everyone has a fair chance of achieving what they want and are capable of - in other words, he described "a politics for the many and not just for the few".
This meant, he said, that there must be an end to "austerity" which was merely a clever way of saying that the many must "go without" while the few made fortunes. He said that pubic services - like the railways or the health service - should not be privatised and run (often inefficiently) for private profit, but should be truly "public" - owned by and serving "the public". It meant that taxation should be paid fairly by those who can afford it so that the country could deliver good health and education for all, as well as effective policing, defence and security.
He said all this, despite the warnings - even from within his own party - that it would mean electoral suicide. He understood that if politicians commit only to what will win the approval of the powerful few, then the voters will quickly understand that the interests of the few will always prevail, and that those of the many must then come much further down the list.
Corbyn's readiness to talk about the issues that matter to most people struck a chord with voters who had been told for years that he was a no-hoper. Bernie Sanders had already demonstrated much the same thing in the US presidential primaries. Left-of-centre parties around the globe - and not least in New Zealand - might at last take note.
Bryan Gould is a former British MP and Waikato University Vice-Chancellor.