Thai police say 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 spokesperson Prawut Thavornsiri told reporters.
Police have not revealed his nationality, although he was caught in possession of a Chinese passport with a birthplace listed as Xinjiang -- home to the country's oppressed Uighur Muslim minority.
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.
Mystery surrounds the alleged bombers' motive but speculation has hardened on links to China's Turkic-speaking Uighur minority.
Thailand deported scores of Uighur refugees to China early in the summer, prompting protests in Turkey where some nationalists hold a deep affinity with the minority group.
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