A Valid Passport
Affidavit of Freedom to Marry under Thai Law:
This is an Affidavit notarized by your Embassy or Consulate stating that you are both free to marry and in effect they have no objection to you doing so. You will be required to visit your Embassy or Consulate in Bangkok to obtain this document and you will each require individual Affidavit.
If you are divorced - a Decree Absolute
If you are a widower - a Death certificate and previous Marriage Certificate.
Proof of income may be required:
This is stated on the affidavits if any income is declared. (Best to check with your Wedding Planner or Tour Operator).
If you are planning to have a prenuptial agreement this will not be recorded by the registrar in Thailand.