Ken Livingstone faces being expelled from Labour when he appears before a misconduct panel over his controversial comments about Adolf Hitler.
London's former mayor will fight for his future in the party at a private hearing in Westminster run by senior officials.
Mr Livingstone was suspended in April last year after claiming that Hitler supported Zionism in the 1930s.
He faces a charge of engaging in conduct that was grossly detrimental to the party.
In a written submission to the hearing, he accused Labour of pursuing the case against him in a ''partisan'' way and suggested there was a witch hunt aimed at critics of Israel.
Mr Livingstone said he had ''raised the issue of the collaboration between Hitler and a section of Zionism in the early 1930s'' as a result of a misunderstanding of presenter Vanessa Feltz's question during a BBC London interview.
He said he had ''no intention'' to cause offence but was ''sorry'' if his remarks did so.
The veteran left-winger said he had taken to the airwaves to defend the reputation of Labour after MP Naz Shah had come under fire for social media posts she subsequently apologised for and admitted contained anti-Semitic language, although Mr Livingstone said they were ''not obviously anti-Semitic''.
He claimed ''supporters of Israel'' had called on Labour to expel him to ''silence'' his criticism of ''Israeli aggression''.
''I did not say or suggest that Hitler was a Zionist. I did not make any equation of Hitler and Zionism. I neither criticised the transfer agreement or the section of Zionism that participated in the agreement."
Mr Livingstone was previously expelled from the party when he announced he would stand as an independent in the London mayoral race after losing the Labour selection process.
It is not the first time he has become embroiled in an anti-Semitism row. In 2006 a High Court judge said he made ''unnecessarily offensive'' and ''indefensible'' remarks likening a Jewish reporter to a Nazi concentration camp guard. But he was cleared of bringing the office of mayor into disrepute.
Ahead of the hearing on Thursday, Mr Livingstone called on his Twitter followers to show their support for him on the social media site.
He said Labour had refused to hold the national constitutional committee hearing in public, despite requests by his lawyers, which include Michael Mansfield QC.
Labour held a review, carried out by Shami Chakrabarti, into racism in the party following comments made by Mr Livingstone and other members.
The former Liberty director, who was later given a peerage by Mr Corbyn and appointed to his Cabinet, found the Labour Party ''is not overrun by anti-Semitism, Islamophobia or other forms of racism''.
But Labour members should ''resist the use of Hitler, Nazi and Holocaust metaphors'', her report said.