Labour sources confirmed Mr Corbyn’s office was involved in Mr Machover’s case but insisted staff made the decision to reverse his expulsion, not the leader himself.
Mr Machover, a member of Hampstead and Kilburn Constituency Labour Party, wrote an article widely distributed to activists at the 2017 Labour Party Conference in Brighton.
He argued that in Labour, a “campaign of equating opposition to Zionism with antisemitism has, in fact, been carefully orchestrated with the help of the Israeli government”.
The essay – ‘Anti-Zionism does not equal antisemitism’ - quoted Heydrich, who said in 1935: “National Socialists had no intention of attacking Jewish people in any way.”
Mr Machover also used quoted Heydrich's pre-Holocaust claim that the Nazi government was "in complete agreement with the great spiritual movement within Jewry itself, so-called Zionism.”
Mr Machover wrote that Heydrich had offered “a friendly mention of Zionism, indicating an area of basic agreement it shared with Nazism”.
The article appeared in a magazine produced by the Labour Party Marxists group, which is closely linked to the Communist Party of Great Britain.
At the time, Labour’s John Mann and Holocaust Educational Trust Chief Executive Karen Pollock both attacked the publication of the article and called for those linked to the group to be expelled from the party.
David Hirsh, a senior lecturer at Goldsmiths, University of London, accused Mr Machover of “monstering of Jews and of Israel” with the Heydrich quote.
Dr Hirsh said a passage in Hitler's Mein Kampf demonises Zionism.
“There should be no place in democratic Labour politics for Mr Machover’s misrepresentation of history," Dr Hirsh added.
In a letter from Labour’s Head of Disputes, Mr Machover was told that the article “appears to meet the International Holocaust Remembrance Alliance definition of antisemitism.”
But the Tel Aviv-born activist was informed that he had been “automatically excluded” from Labour because he was a member of another political party “namely Labour Party Marxists, as well as the Communist Party of Great Britain.”
A letter dated October 5 told him: "For the avoidance of any doubt, you are not ineligible for membership as a result of complaints received by the party that you have breached rule 2.I.8 regarding language which may be prejudicial or grossly detrimental to the party in an allegedly antisemitic article published in your name.
"These allegations are not subject to an investigation as you are not currently a member of the Labour Party.”
Mr Machover won the support of anti-Israel activists along with Labour left-wingers and celebrities including musician Brian Eno.
On October 30, a new letter was sent to him, saying: “The party has reviewed the matters of fact surrounding your case and the decision has been taken to rescind your automatic exclusion from the Labour Party.”
The letter listed the instances of him appearing to support the Communist Party, including 44 articles he wrote in its publication "and primary form of campaigning", and 17 videos of him speaking on the party website.
It added that "any reasonable person" would conclude he had supported the party while a Labour member.
“Such support is incompatible with Labour Party membership, so thank you for clarifying that this was not your intention to provide such support," it said.
“The party would like to urge you to take a cautionary approach towards any actions which appear to be clear prima facie breach of the party’s rules in order to avoid any future misunderstandings.”
Laura Murray, Mr Corbyn’s stakeholder manager at the time, wrote: "There will still be outstanding issues on people’s minds around the reasons for his auto-exclusion, but I am glad that he is now a Labour Party member again.”
But only now has it been confirmed that Mr Corbyn was among those to argue Mr Machover be reinstated to the party.
Since the furore over his article, he has continued to make controversial remarks.
In an interview with an American online news channel he said the "pro-Israel lobby" was exploiting the legacy of the Holocaust to try to silence criticism of the country.
Mr Machover also claimed Israel's Ministry of Strategic Affairs had driven an "immense public campaign" in the UK against Labour's new guidelines on antisemitism.
Appearing at a recent event for the Labour Against The Witchhunt group – which has campaigned to have those expelled by Labour over allegations involving antisemitism reinstated – Mr Machover compared incidents of antisemitism in the Party to the hunt for paedophiles – suggesting eventually someone will be found.
When asked about Mr Corbyn’s intervention over Mr Machover’s expulsion from Labour, a party source told the JC: “Moshe Machover was wrongfully auto-excluded on the assumption that he was a member of another political party, not in relation to any allegations of antisemitism.
“Machover, an eminent Jewish Israeli academic, was not a member of another political party, so should not have been unilaterally auto-excluded by one official, and upon reviewing Machover’s appeal, the party reversed his auto-exclusion.
"Members of the Leader's Office raised concerns about this misapplication of the Party’s rules."
At last year’s Labour Conference in Liverpool, Mr Machover wrote another further article headlined ‘Why Israel is a racist state’.
The article, printed in the same Labour Party Marxists freesheet, said it was “a well-established fact” that the Jewish state is “structurally racist, an apartheid state”.
