“What I’m looking for” by Bardella, 29, was one of the surprise publishing hits of 2024, selling an estimated 140,000 copies across France according to an annual ranking from Express magazine.

MediaTransports, which manages advertising on behalf of the state-owned SNCF rail network, pulled out of a deal to display posters for the book on 500 advertising spots in stations in October last year.

A commercial court in Paris ruled the company was at fault for “wrongful breach of contract”, dismissing its argument that it was compelled by law to “respect political neutrality”.

“Under pressure from SNCF union members, the MediaTransports agency cancelled the promotional campaign for my book that was planned in train stations,” Bardella wrote on X.

“The court has just overruled them: a great victory for freedom of expression against the totalitarian reflexes of the left,” he added.

Promoted to leader of the National Rally in 2022, Bardella is now seen as a possible presidential candidate in elections due in two years’ time after the party’s figurehead, Marine Le Pen, was banned from standing for office last month.

A court found that Le Pen, 56, had overseen a system that embezzled money from the European Parliament in order to employ assistants who were working for her party. She also received a four-year jail term, with two years suspended.

French rail trade union leaders had threatened to take action unless the SNCF blocked the posters of Bardella’s book.

Le Pen and allies regularly accuse the French media and court system of trying to censure them. They have found allies in the new Trump administration, which has openly backed far-right, anti-immigration parties in Europe.

“This ruling further strengthens the protection of rights and freedom of expression,” said Bardella’s publisher, Fayard, which has built up an influential roster of anti-immigration and conservative authors under the ownership of conservative billionaire Vincent Bollore.