The National Legislative Assembly (NLA) on Friday voted to ratify the International Convention for the Protection of All Persons from Enforced Disappearance.
The convention was approved unanimously with 205 members voting in favour during an NLA meeting.
Provisions in Section 23 of the interim constitution required the cabinet to forward the convention to the NLA for deliberation.
By ratifying the convention Thailand officially recognises enforced disappearance committed by state authorities is a crime under international law.
Legal action should be taken against any state official found to be involved in acts of enforced disappearance including abduction, secret imprisonment or concealment of a victim's whereabouts, which are regarded as human rights violations, the convention says.
Severity of punishment vary according to each country.
However, under the convention proper penalties must be devised for those committing enforced disappearances.
Severe punishment must also be brought against those connected with enforced disappearance resulting in death or involving pregnant women, the elderly, the disabled and children, according to the convention.
National Human Rights commissioner Angkhana Neelapaijit praised the move.
However, related domestic laws that correspond with the international convention should be passed as soon as possible so that it can take effect in reality, she said.
"Without crucial domestic laws, nothing can be done in cases of enforced disappearance," she said.
Enforced disappearance, by definition according to this international convention, refers to disappearances caused by government officials, she said.
She called for an independent agency to probe such cases.
"The government must be responsible for the protection of all people. But if authorities are involved in enforcing laws against forced disappearances they could be tempted to conceal information or even the body of a disappeared person," she said.
Ms Angkhana raised the case of her husband Somchai, human rights lawyer from the deep South, as an example. He has been missing since March 12, 2004.
The Supreme Court in 2015 acquitted five police officers accused of abducting Somchai, citing a lack of evidence. Somchai's body has never been found.