The Labour leadership frontrunner had declared that he did not know who Dyab Abou Jahjah was as he angrily dismissed allegations of anti-Semitism.
But he has now conceded the pair had shared a platform at Westminster in 2009, shortly before Mr Abou Jahjah was banned from re-entering Britain by then home secretary Jacqui Smith.
In a statement, Mr Corbyn said: “My staff have researched this and tell me that I did meet this man in 2009 but I have no recollection of him.
“As an MP I have met thousands of people over the years.
“Because I meet them, it does not mean I share their views or endorse their views.”
Photographs have emerged that appear to show Mr Corbyn with Mr Abou Jahjah, who is reported to have told a Flemish magazine in 2004 that he considered “every dead American, British and Dutch soldier a victory”.
The Islington North MP initially said he did not know who Mr Abou Jahjah was but has now admitted meeting him after the controversial figure said it was “beyond doubt” that they shared a platform and were “political friends” who had eaten together at meals.
They spoke alongside each other at an anti-war rally and a debate in a room within Parliament in 2009, shortly after which the radical was blocked from re-entering the UK.
Responding on Twitter to Mr Corbyn’s claim not to know him, Mr Abou Jahjah said: “Whatever reasons made Mr Corbyn say this are for him to know and for us to guess.”
That they shared a platform was “beyond any doubt and is documented and resulted in my ban to enter the UK.
“But maybe he forgot all about it. Who knows.”
He told LBC radio that he had also been present at meals with the MP during the 2009 visit.
“We had, I think, two times lunch or breakfast together so I cannot say that Mr Corbyn is a personal friend but he is absolutely a political friend.”
The left-winger’s campaign to lead Labour has been shrouded in controversy over his alleged dealings with extremists and suggestions that some of his supporters are peddling abuse against Jews on social media.
But as he denied meeting Mr Jahjah in a lunchtime interview, a furious Mr Corbyn insisted he had spent his life fighting all forms of racism and said suggestions he was anti-Semitic were “beyond appalling”.
During a call-in with listeners on BBC Radio 4’s World At One programme, he said: “The idea that I’m some kind of racist or anti-Semitic person is beyond appalling, disgusting and deeply offensive.
“I have spent my life opposing racism. Until my dying day I will be opposed to racism in any form.”
After the call-in, a blog post appearing to be written by Mr Jahjah praised Mr Corbyn’s “openness to dialogue” for making his 2009 visit to Britain possible and saying the controversy made him more determined to come back to the country,
Mr Jahjah rejected suggestions he was guilty of “rejoicing” over the deaths of British soldiers but insisted that “every soldier taking part in an illegal occupation is a legitimate target for resistance”.
He also denied being anti-Semitic - insisting he opposed only Zionism and the policies of the Israeli state.
“I am like Mr Corbyn a socialist, and we do share similar values. This does not mean that I agree with him on everything and I am sure that he also disagrees with me on some things,” Mr Jahjah wrote.
“He was not my cheerleader then and I am not his cheerleader now, serious people do not reason in these terms.
“The subliminal ego of British conservatism is a sewer that stinks to centuries of colonial theft, oppression, murder and lies. And I am catching a tiny bit of that stench right now.
“It makes me more determined to revisit the UK, to speak to people there, and to struggle together for a better future in Europe and beyond.”