The founder of Grace Road Church, Shin Ok-ju, will spend the next six years in prison.
As many as 400 of Shin's followers moved to Fiji, where their passports were seized, and they were forced to endure violent rituals.
The church believes Fiji is the centre of a promised world and will be the one place to escape a looming apocalypse.
But many were forced to work on a plantation or at several church-run businesses, which South Korean prosecutors said were a front for the cult.
Those businesses have won awards and praise from the Fiji government, including lucrative government construction contracts and meetings with the prime minister.
RNZ Pacific understand Grace Road still holds several contracts with the government, including for an extension to the presidential palace and to upgrade the Prime Minister's residence.
The Suwon District Court overnight sentenced Shin to six years in prison, and five other leaders were meted punishment ranging from suspended sentences to 42 months.
RNZ Pacific has approached both Grace Road and the Fiji government for comment.