Thierry Tilly, who was sentenced to eight years in prison by a court in Bordeaux, became a confidante of the landed Vedrines family in 2000 in a case that has both riveted and shocked the nation.
Over nine years, the man who local media dubbed "the guru" manipulated the family of 11 - aged from 16 to 89 - into believing there was a secret masonic plot against their lives, according to court testimony.
Family members were so convinced of his story that they locked themselves inside their chateau for several years, terrified they would be killed. They sold their possessions - including the family manor - and handed over €4.5 million ($5.7 million).
French media reported that the money was poured into a fake Canadian charity that Tilly claimed was set up to pay the Vedrines' "protectors."
The French-born Tilly was convicted of arbitrary detention, using violence against vulnerable people and abusing people weakened by "psychological subjection."
"Eight years is a small price to pay for what he did to our family and children," Christine de Vedrines, a family member who had alerted police to Thierry, told the Sipa news agency on Tuesday. "The trial is behind us and we will do everything to rebuild."
His accomplice, Jacques Gonzalez, was sentenced to four years in prison.
Tilly's lawyer had argued that the family from the 13th-century village of Monflanquin in southwestern France had acted willingly.
"These 11 family members aren't ill, have their feet on the ground, a level of self-awareness. Eleven people manipulated by mysterious forces by a single man? The legal basis for case is weak," lawyer Alexandre Novion told The Associated Press.
Novion denounced testimony about the family's mental state, saying a man's freedom should not depend on "an old Freud tome found in a psychoanalyst's attic." He also said Gonzalez - and not Tillly - was the ringleader and absconded with all the money.
Although Tilly was deemed mentally stable during his trial, French media have reported that he has a history of lies and exaggerations. Tilly claimed before the Bordeaux court that he was a member of the Habsburg dynasty, that he once almost played football for Marseille, and that he knew former French President Francois Mitterrand.
Tilly remained defiant despite the conviction, saying he is a British citizen and will take his case to the European Court of Justice.
"(The trial) has only just begun," Tilly declared.
His lawyer, meanwhile, said he was not aware that his client was a British citizen. But during the time the family was under Tilly's sway, the group apparently moved briefly to Oxford with him. Tilly was arrested in Switzerland.
The case raised echoes of another controversial trial involving France's richest woman, 90-year-old L'Oreal heiress Liliane Bettencourt, who was swindled by a French tax lawyer into handing over a private Seychelles island to him.