The arrests took place on Wednesday at a checkpoint on the Phetkasem Highway in Chumphon province, Pol Maj Gen Pornchai Charoenwong, a regional commander of narcotics suppression police commander, told a news conference on Saturday.
Police arrested Chaliaw Khapanya, 50, and Somnuek Hiamhan, 48, after pulling over their Bangkok-registered silver Volvo and finding 25 kilogrammes of "ice" hidden in the car, he said.
Questioning of the suspects then led police to arrest Liew Kok Yong, 41, a Malaysian national who was waiting to take delivery of the drugs in Hat Yai on Wednesday night. He had arrived in a silver Proton car registered in Malaysia.
Police said Mr Chaliaw told them he had been hired for 400,000 baht to deliver the drugs to the Malaysian. he said he had been introduced to a Malaysian drug cartel by an inmate while serving time at Bang Kwang Central Prison in Nonthaburi.
He and Mr Somnuek obtained the drugs from a trafficker in Suphan Buri on Aug 22 and stored them in Pathum Thani before travelling south as ordered.
Pol Lt Gen Surapol Thuanthong, commissioner of the Narcotics Suppression Bureau, said Mr Chaliaw had been jailed earlier for 19 years for trafficking 11 kilogrammes of heroin. While in prison, he obtained a law degree and was serving as a legal adviser to other inmates before being released.
After his release, Mr Chaliaw delivered "ice" to the Malaysian cartel on four occasions and was paid 400,000 baht each time, the commissioner said.
Pol Gen Pongsapat Pongcharoen, a deputy national police chief, said the drugs had originated from Myanmar and were destined for a big buyer in Penang.
He said that "ice" was in high demand in Malaysia and was priced at 10 million baht per kilogramme there compared with 1 million per kilogramme in Thailand.
The drug cartel was also linked with Pol Lt Col Chamnan Phoomphaijit, a high-profile Chiang Mai officer who had been arrested for methamphetamine trafficking on Aug 18, Pol Gen Pongsapat added.