The Bangkok Criminal Court halved the one-year sentence for Premchai Karnasuta because he pleaded guilty. It rejected his lawyer's request that it commute the sentence to probation.
Premchai was already sentenced in March this year to 16 months' imprisonment for possessing the carcass of an endangered Kajij pheasant and firearms in public areas. He also received a one-year sentence in June for attempting to bribe a park ranger. He remains free on bail on all the charges, paying bail of 200,000 baht ($6,490) in the latest case.
The arms that he was convicted of possessing illegally were found in a police raid on his Bangkok home after his arrest in the wildlife sanctuary in Kanchanaburi province.
Three other hunting companions were found guilty of possessing the panther carcass, but Premchai was acquitted of the charge.
The case fueled public skepticism that justice would be done in a country that has seen the privileged prevail in high-profile cases. Wildlife activists wore black panther masks as a symbol of protest on several occasions and environmentalists have pledged to keep up pressure.
Premchai has one case remaining in the courts, illegal possession of elephant tusks also found during the police raid on his Bangkok home. The verdict in that case is scheduled for Oct. 1.
Premchai's lawyer asked the court to commute his client's sentence, with Premchai pledging to enter the Buddhist monkhood for 15 days to earn merit for those he had wronged.
The lawyer also said Premchai would donate 3 million baht ($97,370) to be used for the public's benefit and would not involve himself with firearms again for the rest of his life.
The court rejected the request because of his prior convictions.