Tommy Robinson's claim that he has been "convicted of journalism" is a "dangerous distortion of the truth", the UK Society of Editors said.
The society, which has nearly 400 members, was referring to the slogan Robinson wore on a T-shirt as he arrived at court ahead of his sentencing for contempt of court over his Facebook broadcast of defendants in a criminal trial.
The English Defence League founder, whose real name is Stephen Yaxley-Lennon, was handed a nine-month sentence at the Old Bailey on Thursday after he was found to have committed contempt of court last week.
Society of Editors executive director Ian Murray said that Robinson, 36, had broken the law by ignoring the contempt laws that any junior reporter working for a reputable news provider would be aware of.
He said: "On the one level this underscores how it is the mainstream media and others that devote huge amounts of time and resources to training their journalists that can be relied upon to provide accurate and balanced reporting of the facts.
"While anyone can claim to be a journalist in this country, and there is no appetite nor should there be for the licensing of journalists in the UK, the mainstream British media adheres to the laws of the land, is correctly regulated and ensures its journalists are highly trained.
"I am not aware that Robinson has any formal training as a journalist, and to claim his trial and sentencing is an attack of journalism itself is a farce.
But he said, while Robinson's claims would resonate with his supporters, the media faced more serious threats such as the proposed Online Harms law, which the society warned offers a blueprint to politicians who wish to silence critics.
Mr Murray added: "Sadly there are people who wish to see the media in the UK emasculated and these sorts of claims are so obviously unfounded they provide ammunition to attack us with.
"Against a background where some politicians who should know better are constantly attacking the free media, Robinson's actions and subsequent claims to represent journalism under attack are a dangerous distraction."