In court papers, Rennert's lawyers described the case as an attempt to twist the story of a successful entrepreneur into "a picture of avarice."
Buchwald argued that at the time of the debt offering, MagCorp was insolvent because of its environmental liabilities.
It filed for bankruptcy in 2001 after the U.S. government sought $900 million in civil penalties.
Rennert's lawyers argued that the environmental liabilities were contingent and unknowable at the time the debt was issued.
"At the end of the day, they understood the evidence and returned a just verdict," Scot Stirling, a lawyer for the trustee, said of the jurors.
The case is Buchwald v The Renco Group Inc, et al, U.S. District Court, Southern District of New York, No. 13-7948. (Addional Reporting by Nate Raymond in New York; Editing by Dan Grebler)