A woman who launched a French version of the #MeToo campaign to expose abusive male behaviour has been found guilty of defaming a media executive she accused of making lewd and sexist remarks.

Sandra Muller said Eric Brion had humiliated her with sexual remarks at a function in Cannes in 2012. She was ordered to pay €15,000 in damages to the executive and €5,000 in legal fees, and was also told to delete a tweet about him and publish the statements issued by the court on her Twitter account and in two press outlets.

Muller, a French journalist based in the US, vowed to appeal. She called the verdict a “backwards step” against the force of an “amazing movement” and said women must “continue the fight”. Her lawyer, Francis Szpiner, said the verdict was out of keeping with current times and a “regression”.

Muller started a viral hashtag in French in October 2017 called #balancetonporc (“expose your pig”), which called on French women to name and shame men in an echo of the #MeToo movement that began in response to allegations that toppled the film producer Harvey Weinstein.

In a Twitter post, Muller had quoted Brion as saying: “You have big breasts. You are my type of woman. I will make you orgasm all night.”

Brion, a media consultant and former head of the TV channel Equidia, acknowledged making inappropriate remarks for which he had apologised by text message the next day. But he sued for defamation, claiming Muller’s post wrongly portrayed him as a sex offender and that the publicity around the incident had ruined his career.

When the hearing opened in May, Brion’s legal team defended his “right to flirt”. Muller defended her right to freedom of expression and said her tweet meant sexist insults would be taken seriously.

Her post led to an outpouring of tales of harassment and assault, which were hailed as helping to confront a culture of permissiveness in France towards unwanted advances.

In a column in Le Monde in 2017, Brion admitted making “inappropriate remarks” to Muller at a cocktail party.

He wrote: “Effectively I did make misplaced comments to Sandra Muller during a drunken cocktail party very late one night, but only once. I liked her. I told her so, heavy-handedly. And only once, I must point out. I don’t want to exonerate myself from my boorishness at the time. I reiterate my apologies.”

But he accused Muller of “deliberately creating ambiguity about what happened” by linking it to the response to the Weinstein affair.

Brion learned of the guilty verdict with a “certain degree of relief and reaffirms he has never harassed Sandra Muller”, his lawyer, Nicolas Benoit, told AFP.

Earlier this year, Denis Baupin, a Green MP and former vice-president of the lower house in the French parliament, lost a defamation suit against six women who accused him of sexual harassment and four journalists who had reported the allegations. His decision to sue for defamation was seen as a backlash against the #MeToo movement in France.