Neil McEvoy has been expelled from Plaid Cymru for 18 months following a party investigation into his conduct.
Plaid Cymru said the South Wales Central AM had breached a series of party rules.
It found him guilty of misconduct over his behaviour at the 2017 Plaid Cymru spring conference.
Mr McEvoy said the process was "completely flawed from the very beginning" and that he intended to appeal against the decision.
The AM has already been expelled from his party group in the assembly - meaning he sits as an independent in the Senedd chamber.
The timing of the expulsion means that he will be unable to be reselected as a South Wales Central candidate for Plaid for the next assembly election in 2021, Mr McEvoy told BBC Wales.
It marks the end of a process that began about a year ago.
Analysis by Aled ap Dafydd, BBC Wales political correspondent
After being criticised for taking so long, Plaid Cymru have finally come to a decision on Neil McEvoy.
The party's standing orders didn't allow for a permanent expulsion and a temporary exclusion gives the impression that the door is still ajar.
But it's very possible, barring a successful appeal, that Neil McEvoy has been dealt a potentially career ending blow by his party.
He could be in exile when prospective candidates battle it out for the regional list nomination. Neil McEvoy might never stand for Plaid again but the party hasn't heard the last of him either.
The man suspended for his conference arrival last year will be there again this year, albeit under very different circumstances.
Plaid Cymru said on Monday that a disciplinary panel had resolved to exclude Mr McEvoy from the party for 18 months.
It said it had heard four complaints, three of which were upheld.
"These included actions or statements damaging, or potentially damaging, the public reputation of the party, and breaches of confidentiality," a statement from the party said.
It said the panel had found him guilty of misconduct over his actions during the 2017 Plaid Cymru spring conference.
Specifically, the panel found him guilty of conduct in party meetings or against party members during party-organised events, or in correspondence dealing with party business, that was intimidating, harassing or that caused distress or disillusionment among party members and/or staff.
"The exclusion reflects the gravity of the cases put before the Panel," the statement continued.
"Neil McEvoy will have the right to appeal the decision with a formal submission to the Party within seven days."
The spring conference in 2017 came days after a tribunal found that a remark Mr McEvoy made to a Cardiff council officer amounted to "bullying behaviour" - leading to him to being suspended for a month.
According to copies of complaints against Mr McEvoy, Plaid chairman Alun Ffred Jones said he had asked the AM to not hold a rally at the spring conference, a request that was ignored when a welcoming party greeted Mr McEvoy at the Newport venue.
He was asked by Mr Jones not to make any reference to the tribunal in his speech to conference, but Mr Jones said Mr McEvoy made frequent references to it.
"Mr McEvoy... did everything possible to take attention away from the Conference message so that the Leader and others were on the back foot answering questions on this issue rather than on Plaid's message for the forthcoming elections," Mr Jones wrote.
Another complaint, from Plaid Cymru chief executive Gareth Clubb, criticised Mr McEvoy for breaching the confidentiality of the disciplinary process.
He said it had caused "great distress" that Mr McEvoy had revealed details of complaints about his behaviour - not related to the Spring event - at a press conference in January.
'Abuse of process'
In response, Mr McEvoy said: "Plaid members need to know that I have been expelled from the party for 18 months for being welcomed at a conference by members and for not allowing the Chair to change my conference speech.
"Freedom of speech and association are fundamental human rights which Plaid members fight to uphold."
He claimed to have evidence that Mr Jones had begun the investigation into him before any written complaints were received and that "others were aware of the complaints, whilst I was not".
"This is an unbelievable abuse of process," Mr McEvoy said.
"There has been no due process or natural justice, just a sustained effort by lobbyists to undermine me," he added.
"The complaints have not been dealt with in accordance with the party's own rules and standing orders."
Accusing Plaid Cymru of breaching his human rights, and not allowing him legal representation, Mr McEvoy said: "I will obviously be appealing this disgraceful decision."