The former leader of a purported self-help group has been convicted of charges that centred on details of what prosecutors called a secret society of “sex slaves” within a community of followers in upstate New York.

A jury in federal court in Brooklyn took less than five hours to find Keith Raniere guilty on all counts of sex-trafficking and other charges accusing him of coercing women into unwanted sex using systematic shame and humiliation.

“Raniere was truly a modern-day Svengali,” Brooklyn United States Attorney Richard Donoghue said outside court, calling the former self-help guru a lying manipulator who “ruined marriages, careers, fortunes and lives”.

Raniere listened attentively, but showed no reaction as he learned the verdict.

His lawyer, Marc Agnifilo, said Raniere plans to appeal.

“Keith maintains his innocence. It’s a very sad day for him,” Mr Agnifilo said.

“I think he’s not surprised, but he maintains that he didn’t mean to do anything wrong.”

Raniere’s sentencing is set for September 25.

Raniere once had an international following with a foothold in Hollywood with his self-help group, called NXIVM, that was deemed a cult by critics.

His adherents included TV actress Allison Mack, best known for her role as a friend of a young Superman in the series Smallville; a Seagram’s liquor fortune heiress, Clare Bronfman; and a daughter of TV actress Catherine Oxenberg of Dynasty fame.

“This was a very frightening group,” Ms Oxenberg said after the verdict.

Her daughter India left NXIVM after her mother became an outspoken critic of it.

“I had to save a child who was caught in the grips of this cult, so I wasn’t going to stop until I succeeded,” Ms Oxenberg said.

Prosecutors had told jurors that Raniere — a man known as “Vanguard” and revered as “the smartest man in the world” among some followers — was actually a creepy con man who barely got passing grades in college.

The sorority, sometimes called “The Vow”, was created “to satisfy the defendant’s desire for sex, power and control”, Assistant US Attorney Moira Penza said in closing arguments.

Among the more damning allegations against Raniere were that he had some women branded with his initials and that he started having sex with one of his followers starting at age 15.

Prosecutors said he took a series of nude photos of the teen that were shown at trial, one by one, to the eight women and four men who comprised the jury.

The defence argued Raniere was a genuine believer in unconventional means for self-improvement and that all his sexual encounters with female followers of NXIVM were consensual.

His behaviour could be seen as “repulsive and offensive, but we don’t convict people in this country for being repulsive or offensive”, Mr Agnifilo said in his closings.

Raniere, 58, was arrested at a Mexican hideout in 2018 following an investigation his Albany-area group.

His organisation began to crumble amid sensational reports about The Vow alleging its members were held down and branded in ceremonies at a “sorority house” for them that had a mock dungeon.