Ken Livingstone says he has been suspended from the Labour Party for one year over controversial comments about Adolf Hitler and Zionism, following a disciplinary hearing in London.
The former London mayor - who has been suspended from the party since April last year - had threatened to launch a judicial review if he was expelled from the party.
After being found guilty of engaging in conduct that was "grossly detrimental" to the party, Mr Livingstone slammed the decision and said he would now consult with lawyers about his legal position.
The ex-mayor earlier said he had expected to be expelled because the panel investigating the case was dominated by "right-wingers".
Mr Livingstone said: "Today's Labour Party panel extended my suspension for another year because of my political views, not because I have done anything to harm the Labour Party.
"The Labour Party's disciplinary process was not in accord with natural justice in a number of ways. For example the panel hearing was not held in public, despite the fact that it could have been under Labour's rules. I was suspended for more than 11 months before the hearing was held.
"Scheduling the final day of this disciplinary hearing, on the day the Labour Party launched its campaign for the May 4 elections, was a supreme misjudgment by whoever planned this in the Labour Party headquarters.
"It was clearly not in Labour's interests as the hearing will inevitably generate unfavourable headlines at a time when Labour should be focused on campaigning.
"I will be launching a campaign to overturn my suspension of party membership."