Spokesman Matt Hershey says Donald Lapre was found dead in his cell at a Florence facility Sunday morning. His trial was scheduled to begin Tuesday.
Hershey says the death remains under investigation.
A grand jury indicted Lapre in June on 41 counts of conspiracy, mail fraud, wire fraud and promotional money laundering. He was accused of overseeing and promoting the opportunity through his company called "The Greatest Vitamin in the World."
The government says at least 220,000 victims in the scheme were defrauded of nearly $52 million.