The blast at the Erawan Shrine in an upscale shopping district left 20 dead and more than 120 injured. A second bomb detonated a day later, but there were no reports of injuries.
" Preliminary investigation shows that he is related to both bombings," Prawuth said.
The suspect is a foreigner, but officials declined to say which country he is from.
"We found dozens of passports inside his room. We have to check which nationalities they belong to," deputy police chief Chakthip Chaijinda said, according to the Bangkok Post.
Chakthip said it is not yet clear whether the man detained is the one seen wearing a yellow T-shirt and leaving a backpack under a bench just before the explosion at the shrine. Police have said they believe more than one person carried out the attack.
"He didn't do it alone, for sure. It's a network," national police chief Somyot Poompanmoung said.