The former vice-chair of Momentum Jackie Walker has been expelled from the Labour party for misconduct, in one of the longest-running high-profile cases of the party’s antisemitism crisis.

It is understood the party disciplinary process took into account a pattern of behaviour by Walker over time, including comments on social media. She was expelled for “prejudicial and grossly detrimental behaviour against the party”.

Walker was suspended more than two years ago after comments made at an antisemitism training session, where she criticised Holocaust Memorial Day for only commemorating Jewish victims.

After participants said the event does in fact commemorate other genocides, Walker said that was not how she viewed it. “In practice, it’s not actually circulated and advertised as such,” she said. “I was looking for information and I still haven’t heard a definition of antisemitism that I can work with.”

During the training event, Walker also questioned why Jewish organisations, including schools, said they needed high security.

The event, which took place at the Labour party conference, was secretly filmed and then leaked to the media, leading to Walker’s suspension from the party. Walker has since made a film called Witch Hunt about her experiences.

Walker was previously suspended and then readmitted to the Labour party after posting during a Facebook discussion that Jews were “chief financiers of the sugar and slave trade” and arguing that “the Jewish Holocaust does not allow Zionists to do what they want”.

She was readmitted to the party after an investigation but removed from her post in Momentum after her second suspension.

Her case was referred by Labour’s governing national executive committee to its highest disciplinary body, the national constitutional committee (NCC), the party’s only body with the power to expel members.

A Labour spokesperson said: “The NCC has found that the charges of breaches of party rules by Jackie Walker have been proven. The NCC consequently determined that the sanction for this breach of the rules is expulsion from Labour party membership.”

Walker’s case, which has been repeatedly delayed, was heard by an NCC panel in Deptford, south-east London, on Tuesday, though Walker left the hearing mid-morning saying she had been refused the chance to give an opening statement because party rules insist it must be given by her legal representative.

Walker, who said she had submitted more than 400 pages of evidence in her defence, addressed a small crowd of supporters from Labour Against the Witchhunt outside the hearing and said it had “only confirmed my worst fears about the process”.

In a statement, Walker said: “After almost three years of racist abuse and serious threats; and of almost three years of being demonised, I was astounded that the Labour party refused to allow me a few short moments to personally address the disciplinary panel to speak in my own defence. What is so dangerous about my voice that it is not allowed to be heard?

“All I have ever asked for is for equal treatment, due process and natural justice; it seems that this is too much to ask of the Labour party.”

The party keeps the identity of the panel hearing the case confidential but the Guardian understands that Russell Cartwright, an employee of the Labour MP Kelvin Hopkins, is among the three who heard Walker’s case. Hopkins is awaiting a similar NCC hearing on allegations of sexual harassment.

The other members of the Walker panel are understood to be Alan Tate from the CWU trade union and Anna Dyer, one of the representatives elected from local parties.

A spokesperson for the Jewish Labour Movement said it was “a clear and unambiguous case of prejudicial and grossly detrimental behaviour against the party” but said the expulsion had come “two and a half years too late” and suggested Walker’s case had been repeatedly delayed.

“In the intervening time, Ms Walker and others have been key to perpetuating a culture of denial and obfuscation,” the group said.

Labour’s general secretary, Jennie Formby, told MPs last month that the party had investigated 673 alleged cases of antisemitism and expelled 12 party members, with six receiving other sanctions, since last April. Five others referred to the NCC have left the party of their own accord.

• This article was amended on 28 March 2019 to correct an editing error that placed reported speech in direct quotes.