0932 GMT February 18, 2020
Police said the suspect, Yusufu Mieraili, was arrested last week near the border with Cambodia.
"We have informed him of the charge. He acknowledged and confessed to the charge," national police spokesman Prawut Thavornsiri told reporters, AFP reported.
Police have not revealed his nationality, although he was caught in possession of a Chinese passport.
A second man identified as Adem Karadag has already been charged over the crime after he was caught in a flat in a Bangkok suburb with bomb-making paraphernalia and dozens of fake Turkish passports.
Police have said neither man is thought to have physically planted the bomb on August 17 at a religious shrine in downtown Bangkok that killed 20 people.
But they are confident the pair are involved in the network blamed for the attack, which rocked the capital and dented faith in Thailand's key tourist sector.
After nearly two weeks without progress on the bombing, police made what they said was a breakthrough following a raid on the flat in Bangkok's eastern suburbs.
There they found Karadag. That arrest led to Mieraili who was picked up three days later on the Cambodian border.
The alleged confession of one of the gang's key members came as police said they had also issued two new arrest warrants.
The total number of people wanted for suspected involvement in the deadly attack stands at eleven -- on top of the two arrested foreigners.
Prawut told reporters one of the new warrants is for a foreign man of unknown nationality called Abdullah Abdullahman.
The second is for an unnamed foreigner seen on CCTV buying items from a department store close to where the two arrested suspects allegedly stayed.
Prawut said the new warrants were based on witness testimony and the interrogation of the two arrested men.
Both men are wanted on a charge of illegal possession of explosives, he added.
The shrine that was hit by the blast is known for its popularity among Chinese worshippers.
The majority of those killed in Thailand's worst single mass casualty attack were ethnic Chinese visitors from across Asia.
The Chinese visit Thailand in far greater numbers than any other nationality. Tourism accounts for at least 10 percent of GDP and remains one of the few economic bright spots in the junta-run kingdom.