Narongrit Suksarn, 29, from Nakhon Si Thammarat, surrendered to the Technology Crime Suppression Division (TCSD). He pleaded his innocence and claimed that he was smeared by the "Unlimited Hack Team," a group of hackers to which he formerly belonged but now is no longer a member.
The Unlimited Hack Team earlier posted a message on its Facebook page denying any involvement in the hacking.
Mr Narongrit said his surrender was intended to prove his innocence. He also offered to help police with technology to improve the security of the PM's office computer system against hacking.
Mr Narongrit's home and his computer was to be checked thoroughly by the police to collect possible evidence, said TCSD chief Pol Maj Gen Pisit Pao-in.
About 20 hackers are being targeted by the police investigation as they have potential to intrude into the servers of many websites, according to the TCSD chief.
The police have not yet found any clues indicating that a major political party was behind the hacking, as had been alleged.
The homepage of the Prime Minister's Office website was hacked on Wednesday (May 8), with the hacker leaving disdainful messages on the home page, parodying Prime Minister Yingluck Shinawatra.
Opposition Democrat Party leader and former prime minister Abhisit Vejjajiva brushed aside an attempt to link his party with the suspect – Nakhon Si Thammarat is a major stronghold of the Democrat Party.
He voiced his support for the government taking legal action against the wrongdoer in the hacking case. He also urged the government to take similar action against other offenders in other computer-related cases.
As this story was posted, the website of the Office of the PM was still offline.