In Thailand, the concept of attorney-client privilege is an obligation and right of the licensed lawyer not to disclose the client's confidential information. There are no legal concepts that grant such obligations and rights to the client itself. Thus, copies of attorney-client communications which are held by the client may not be protected (although there may also be an argument that copies that are held by the client should remain protected by privilege, there is no clear legal precedent to support this position).

In-house lawyers should be treated in the same way as external lawyers. Their communications and work product should therefore be protected by attorney-client privilege in respect of the legal work provided to the in-house client. However, in-house lawyers must have a lawyer license under the Lawyer Act, or their communications and work product will not be protected by attorney-client privilege pursuant to the Lawyer Act or the Civil Procedure Code.

Notwithstanding the above, in the absence of clear precedent, there may also be an argument as to whether attorney-client privilege should extend to in-house lawyers. However, this may also be dependent on the role in which the in-house lawyer undertakes (i.e., whether the communication or work product relates to genuine legal advice). Ultimately, this may therefore be a question of fact on a case-by-case basis.

It may be possible for the principle of attorney-client privilege to extend to internal communications between in-house lawyers. The foregoing may be especially true where the in-house lawyers possess lawyer licenses and where such communications relate to the legal work provided to their in-house clients.

As attorney-client privilege only applies to licensed lawyers under the Lawyer Act, communications between clients and foreign lawyers will not be protected by attorney-client privilege pursuant to the Lawyer Act or the Civil Procedure Code unless the foreign lawyer is licensed under the Lawyer Act. However, this is not normally the case.

Whether or not a nonlegal professional is able to claim privilege will depend on their status. This is because the law clearly outlines which types of person are under the obligation and/or have the right to protect the client or customer's information.

For example, the Lawyer Act and the Civil Procedure Code restrict the obligation and right to lawyers; the Criminal Procedure Code provides the obligation and right to persons who have obtained the information in connection with their profession or duties; and the Penal Code specifically states, amongst other matters, that an offense relating to the disclosure of information may be committed by those who are physicians, pharmacists, drug dispensers, midwives, nurses, priests, advocates, lawyers or accountants, or those who assist or are receiving training in such professions.

Additionally, the obligation not to divulge confidential information may be imposed on other professions under other specific laws, such as the obligations of accountants under the regulations of the Federation of Accounting Professions.