Writer and activist Owen Jones has said that it is "a tragedy" Ken Livingstone finds himself on the brink of being expelled from the Labour Party.
Describing Mr Livingstone's remarks over Hitler and Zionism as "totally unacceptable", Mr Jones insisted that the former Mayor of London’s record in office was good.
Addressing a packed meeting of the Jewish Labour Movement on Sunday, Mr Jones said: "It is a tragedy what has happened to Ken Livingstone. He did achieve good things as Mayor of London.”
Mr Jones added that it was important that people like himself who are not Jewish "stand in solidarity" with those who are, to "confront Ken Livingstone and others who make unacceptable comments."
He also said that it was vital the Jewish contribution to the Labour Party was always recognised. Without Jews, he continued, "the Labour Party would not exist."
Mr Jones said he remained "a passionate" campaigner for Palestinian self-determination but wanted a two state solution in which Jews and Palestinians lived in peace and with security.
"We are never going to peace in the Middle East when Jews and Palestinians do not feel safe," he said. "This can only came about through dialogue. There can be no military solution."
Asked about the current crisis in the Labour Party, Mr Jones refused to say who he would like to be leader.
But he added: "I would struggle to sum up now what Labour's message is. I don't think they have a clear vision or policies. Most people have a much clearer idea of what Theresa May represents than they do Jeremy Corbyn."
Mr Jones had received criticism for addressing the JLM from far-left extremists. He said he had quit Twitter to avoid abuse accusing him of being "a stooge of the Israeli state."
He added that on the left there is "a minority where antisemitic tropes are encouraged or ignored.”
"The menace of antisemitism," he said, "needs to be driven out."
Mr Jones also claimed that Momentum founder Jon Lansman was an example of someone on the left who had stood up to Mr Livingstone by calling for him to leave politics.
He added:"We have got Ken Livingstone and Jackie Walker whose comments are unacceptable. I have called for Jackie Walker's expulsion but her partner Graham Bash was someone who was something of a mentor to me. I was close to him - but now that has changed."
Mr Jones attacked Israeli PM Benjamin Netanyahu, describing his government as "hard right and violating international law."
Mr Netanyahu, he said, "now has the fanatical support of Donald Trump" and this is "making a peace process impossible."
He added that those who stood up to Mr Netanyahu were "increasingly portrayed as the enemy within."
He said a friend of his from a family of Holocaust survivors had gone to Israel to do charity work.
"She risked being criminalised by the government for trying to work with Palestinians and Jews alike. This is unacceptable. You can see echoes with Trumpism where dissent is treated as treason.
"You can see this taking place in Israel to people who believe inequality. Those are the people I want to stand and unite with - not the likes of Benjamin Netanyahu and the associates of his who are riddled with bigotry."