The Green Party discriminated against former deputy leader Dr Shahrar Ali because of his gender critical beliefs, a court has ruled.
Dr Ali launched legal action against the Green Party of England and Wales, the first of its kind, after being forced out of his role.
The Green Party admitted "procedural shortfalls" in dismissing Dr Ali.
The Mayor's and City County Court judgement awarded £9,100 in damages to Dr Ali.
All other allegations of discrimination and victimisation by the Green Party were dismissed.
The party removed Dr Ali as spokesman for policing and domestic safety in February 2022 for repeated breaches of the party's Spokespeople Code of Conduct.
In papers submitted to the court, lawyers acting for Dr Ali claim that officials in the Green Party "collaborated" to remove him from his post because of his beliefs about gender, which include the view that "biology is real and immutable".
The court found Dr Ali was removed in a "procedurally unfair" because they failed to identify any code breaches when dismissing him.
Dr Ali called the result a "landmark case".
Speaking outside the court, Dr Ali called for the Equality and Human Rights Commission to investigate the Green Party over how it handles trans rights debates.
Alongside this, he said independent inquiry "into the hostile environment in political parties across the left" should be set up.
He said: "The current Green Party of England and Wales is out of control.
"Parties are not beyond the law when it comes to seeking to discipline their representatives in accordance with their own rules for alleged misconduct."
In a statement, the Green Party said it "acknowledges that there were procedural shortfalls in how we deselected one of our spokespeople".
The party added: "We apologise for failing in this instance to live up to the standards that both we and the court expect."