Laurence Fox libelled two people when he referred to them as "paedophiles" on social media, a High Court judge has ruled.
The actor-turned-politician, 45, was sued by former Stonewall trustee Simon Blake and drag artist Crystal over a row on X, formerly Twitter, in October 2020.
Mr Fox used the term against Mr Blake and the former RuPaul's Drag Race contestant - real name Colin Seymour - in an exchange about a decision by Sainsbury's to celebrate Black History Month.
The Lewis star counter-sued the pair and former Coronation Street actress Nicola Thorp over tweets which accused him of racism.
In a ruling on Monday, High Court judge Mrs Justice Collins Rice ruled in favour of Mr Blake and Mr Seymour and dismissed Mr Fox's arguments.
She said: "Mr Fox's labelling of Mr Blake and Mr Seymour as paedophiles was, on the evidence, probabilities and facts of this case, seriously harmful, defamatory and baseless.
"The law affords few defences to defamation of this sort.
"Mr Fox did not attempt to show these allegations were true, and he was not able to bring himself on the facts within the terms of any other defence recognised in law."
Patrick Green KC, representing Mr Fox, previously argued that neither Mr Blake nor Mr Seymour had "suffered any actual, real-world consequences" due to the actor's tweets.
Mr Fox told the court he was "horrified" when he saw he had been called a racist, which he later described as "a career-ending word and a reputation-destroying allegation".
The actor-turned-founder of the Reclaim Party said he faced a "significant decline" in the number and quality of roles he was offered after he was accused of being a racist.
Lorna Skinner KC, representing Mr Blake, Mr Seymour and Ms Thorp, said the trio "honestly believed, and continue honestly to believe, that Mr Fox is a racist".
Mrs Justice Collins Rice did not make a ruling on whether or not Mr Fox was "a racist".
"I am very much aware that Mr Fox would have liked to leave court with a clear determination that he 'is not a racist', Ms Thorp with a determination that it is substantially true that he is, and Mr Blake and Mr Seymour with an endorsement that at least they genuinely thought so, and an honest person could have thought so too," she said.
"But the entire case is, in that sense at least, all about contested views of what does and does not amount to being 'a racist'."
Speaking outside court, Mr Fox expressed disappointment that the judge had not made a ruling on the meaning of the word "racist".
He described the decision as a "nothingburger" - defined as something insubstantial or lacking in substance - and said he planned to appeal.
In a statement on X, Ms Thorp said: "For the last three years, Laurence Fox has held us responsible for the downfall of his acting career, his failure to become London Mayor and even the increasing cost of his car insurance.
"All because on 4 October 2020 we exercised our right to free speech by expressing our honestly held opinions.
"It's time that Mr Fox accepted that any damage to his reputation is entirely his own doing."