Judge Susan Coleman approved a request by the county medical examiner's office to exhume the body of Urooj Khan, who died in July 2012, the Chicago Tribune reported.
Khan's death had been attributed to natural causes but toxicological tests -- resulting from a tip to authorities -- found levels of cyanide in his blood.
Khan's widow, Shabana Ansari, said Thursday she supported the exhumation, saying she believed it would "reveal the truth," WLS-TV, Chicago, reported.
Khan is survived by his wife and a teenage daughter from an earlier marriage. His lottery winnings are in probate because Khan's brother has said in court documents he wants to ensure the daughter receives her share of the assets.
Khan's first wife, Maria Jones, who lived in Indiana, told the Chicago Sun-Times Thursday she had not seen her daughter, Jasmeen Khan, in 13 years.
She and Khan divorced in the late 1990's, and Jones said Khan had forcibly taken their child to India.
"I don't know if she knows I'm still alive," Jones said.