Former foreign affairs minister Noppadon Pattama has been acquitted of malfeasance in a case involving the Preah Vihear temple communique he signed in 2008.
The Supreme Court's Criminal Division for Holders of Political Positions on Friday voted 6-3 to dismiss the case filed by the National Anti-Corruption Commission (NACC).
The nine justices decided the communique was not a treaty so it did not require prior review by parliament as required under Section 190 of the 2007 constitution.
They also said the accusations that Mr Noppadon had abused his power and that he deliberately caused Thailand to lose interests had no grounds.
Mr Noppadon, who was foreign minister in 2008 when the late Samak Sundaravej was prime minister, said after the ruling he felt as though he had been pulled out of hell after being accused of having “sold the nation” for years.
“I forgive all sides and will not sue them back,” he said.
In 2013, the anti-graft body, which also handles abuse of authority of malfeasance cases, filed the suit against Mr Noppadon, accusing him of violating Section 157 of the Criminal Code on malfeasance.
It acted on a Constitutional Court ruling on a complaint filed by the Democrat Party, which sought to nullify the document and accused Mr Noppadon of failing to submit the communique to parliamentary scrutiny before signing it as required by Section 190 of the then 2007 constitution.
Section 190 provides that a treaty which will result in a change in Thai territories needs to be approved first by parliament.
Mr Noppadon, who denied the charge as well as others related to it, claimed that since the communique did not result in a change to Thai borders, he did not violate Section 190.
The Constitutional Court ruled in the Democrat Party's favour, saying the communique "might" result in a change in the territory. The NACC therefore sought to impeach and prosecute Mr Noppadon.
The Senate, however, did not impeach him as recommended by NACC as the votes fell short of what was required.
The criminal case was forwarded to the attorney general, who dropped it. The NACC then filed the case with the court by itself.
The case dated back to 2008 and rekindled a century-old border conflict between Thailand and Cambodia. It involves the ownership of 4.6 square kilometres of land around the ancient temple over which both countries claimed. The International Court of Justice ruled in 1962 that the temple itself belonged to Cambodia.
In 2008, Cambodia applied to list the temple as a Unesco heritage site. Mr Noppadon negotiated with Cambodia on a revised map which was later endorsed by the Thai National Security Council.
Both sides signed a joint communique on June 18, 2008.
The issue turned political when the People's Alliance for Democracy claimed the agreement was made in exchange for benefits for businesses owned by former premier Thaksin Shinawatra in Cambodia. Mr Noppadon was one of Thaksin's lawyers.