Sukhwinder Singh Dhillon, 54, poisoned his wife, Parvesh Kaur Dhillon, on February 3, 1995, and business partner, Ranjit Singh Khela, on June 23, 1996.
Dhillon was serving a 25-year sentence for first-degree murder at Warkworth Institute since 2001. The cause of Dhillon's death yesterday was not released.
Death of both of his victims were originally believed to be of natural causes until toxicology tests revealed strychnine in their bodies.
Dhillon collected USD 300,000 in insurance after his wife died, and was making a claim for USD 200,000 from Khela's life insurance policy when he was arrested, the Sun News Network reported.