Nxivm founder Keith Raniere was convicted last year of racketeering, sex trafficking, child pornography possession and other crimes.
As leader of the group he recruited women as slaves and forced them to have sex with him.
Prosecutors said the 60 year old should spend his life behind bars for the "immeasurable damages" he caused to victims of the cult.
District Judge Nicholas Garaufis also fined Raniere $1.75m (£1.34m) at the sentencing hearing in Brooklyn on Tuesday.
Raniere himself never took the stand during the case last year. He was the only member of Nxivm's leadership to face trial as others took plea deals.
His lawyers have maintained his innocence throughout and have blamed a "media campaign involving witnesses who were motivated to testify falsely" for his conviction.
US authorities began investigating Nxivm - pronounced nexium - after the publication of a New York Times investigation in 2017.
Based in Albany, New York and created in 1998, the group described itself as a "community guided by humanitarian principles that seek to empower people".