The court also handed down a 25-year-plus sentence to his youngest son.
Supat was sentenced in absentia after jumping bail following his release in July last year. An arrest warrant was issued for him in February after he failed to appear for a court ruling in the murder case.
Thai media reported the doctor-turned-murderer was recently spotted at a hotel in Cambodia.
The prosecution indicted Supat and sons Ake and Akara on charges of murdering a Myanmar man and hiding his body.
The charges stemmed from the death of a male migrant worker named Ita whose body was buried in Supat’s pineapple plantation in in Phetchaburi’s Tha Yang district.
The prosecutors alleged Supat shot dead his employee because he suspected him of having an affair with Supat’s wife, Wilasa Chantarabanchorn.
The court said it found the testimony of two Myanmar witnesses and DNA evidence from the victim’s skeleton convincing, and handed death sentence to Supat and his eldest son, Ake.
The court initially imposed death sentence on Akara, the younger son, but reduced the penalty to 25 years and three months because the defendant was a minor when the murder took place.
The court is considering bail applications filed by Ake and Akara who want to appeal the ruling.
Ita’s remains were among three human skeletons unearthed in the orchard in 2012 by investigators searching for a missing couple suspected of also being murdered by Supat. Why he would have murdered the other two has not been revealed.