Smallville star Allison Mack pleaded guilty to playing a part in an alleged scheme to turn women into sex slaves for a cult-like upstate New York group.
Mack, 36, conceded to two racketeering counts and faces up to twenty years in prison for each when she is sentenced on September 11.
Through tears she apologised to the women that prosecutors say were exploited by Keith Raniere and the purported self-help group called NXIVM.
"I believed Keith Raniere's intentions were to help people, and I was wrong," Mack told a Brooklyn judge, on the same day jury selection began for a federal trial in the case.
Mack, who is best known for her role as a young Superman's close friend on the series Smallville between 2001 and 2011, said: "I know I can and will be a better person."
The plea means Mack will avoid going to trial with Raniere, wealthy heiress Clare Bronfman and another member of Raniere's inner circle, Kathy Russell.
They have all pleaded not guilty and denied any wrongdoing.
About two hours after Mack's guilty plea, potential jurors got their first glimpse of the jailed Raniere.
Opening statements are scheduled for April 29 for a trial that is expected to last up to six weeks.
Court papers allege NXIVM formed a secret society of women who were branded with Raniere's initials then forced to have sex with him.
Attorneys for the defence insist any relationship between Raniere and the alleged victims, including an unidentified actress and other women expected to testify against him at trial, was consensual.
On Monday Mack said she obtained compromising information and images of two unidentified women at Raniere’s instruction.
She said this was called "collateral" within the group and she threatened to make public if they didn't perform "so-called acts of love."
