In the packed Paris courtroom, the corporate magnate portrayed himself as a successful business leader who had labored to turn LVMH into the world’s top luxury conglomerate, with 75 brands, including Louis Vuitton and Dior, and 200,000 employees worldwide. When Mr. Arnault first took over the company in the 1980s, it had just 10,000 employees.

He denied ever knowing of any illegal surveillance.

Mr. Squarcini was tried alongside nine other defendants — mostly civil servants, police officers and consultants. Two of them were found not guilty.

As the main defendant in the case, Mr. Squarcini was convicted of myriad offenses, including mishandling classified information and complicity in the unauthorized activity of a private investigator. He was found not guilty on a range of other charges.

In its verdict, the court said Mr. Squarcini had, in particular, “misappropriated state resources in order to satisfy the clandestine concerns” of his key client, LVMH.The court added that Mr. Squarcini had “designed and validated a system of close surveillance” of Mr. Ruffin and a satirical publication that he headed, Fakir, whose staff members helped make the film, “Merci Patron,” which portrayed Mr. Arnault as a symbol of corporate greed.

“The court handed down severe sentences, but with a severity commensurate with the seriousness of the attacks made by Mr. Squarcini and his acolytes on freedom of the press, freedom of expression, the rights of Francois Ruffin and the rights of the Fakir newspaper,” Benjamin Sarfati, Mr. Ruffin’s lawyer, said in an interview on Thursday. “But we would have liked LVMH to be on trial, because the people convicted today acted at LVMH’s request,” he added.