How do I register a Thai marriage in Malaysia?

A marriage abroad must be registered in Malaysia through your state's religious affairs office or Syariah Court. In general the steps are:
1. Obtain the marriage certificate from the relevant provincial Islamic Council in Thailand.
2. Have the certificate verified at the Consulate General of Malaysia in Songkhla (or the relevant Malaysian mission).
3. Take the documents to the state Islamic Religious Department to apply for registration.
4. If issues arise (polygyny without permission, wali, witnesses), you will be referred to the Syariah Court for validation of the marriage, and possibly prosecution.
State enactments usually set a period for registration (commonly six months); late registration can be an offence. Check the state-by-state guide and marriage abroad.