If you married in Thailand then your have to register the marriage in Thailand. This is the Thai marriage registration process. As a foreigner you need a obtain a few things as the process for marriage registration in Thailand is very simple. The first process starts with your local Embassy in Thailand. We have listed a number of them on this website. What you need from them is a 'letter of no impediment' which states that you are single and can get married in Thailand.
You can normally email them and ask them to email you a copy so you can complete it at home and then take it in to the Embassy when completed. This is normally a two day process so don't go on a Thursday or Friday if you are outside of Bangkok as you would have to wait until the Monday for the letter. Its a simply form and each Embassy has their own version of the form. Complete this, take it in to your Embassy and wait until they are complete.
IF you are divorced or your former spouse died you need to give them certified copies of either the death certificate or the divorce decree so they can issue the letter for you. Once you get the letter back you need to go to the Thai Ministry of Foreign Affairs in Laksi. They will then take the letter and check to see if the letter is real or fake. This takes about 4-5 hours so do go early as the traffic in Laksi is horrible. They will then give you the letter back with a small stamp on the back of the letter to show that it has been verified. There is a map below with their contact details. They are on the second floor of the building. Simply tell the taxi driver 'CAT Telecom Laksi' as eveyone knows where that is. The Foreign Affairs Department is about 200 meters from there.
Once this is done you need to take the letter to the local Amphur's Office (District Office) and they will then complete the forms and issue you with a Thai marriage certificate. This takes about 30 minutes to complete. There are 2 certificates. There is one that looks like a diploma and also a multipage one. You need to keep both of them safe as you will need copies of both if you plan on applying for a Thai marriage visa later at a Thai Embassy. The best and most foreigner friendly Amphur is the Amphur in Bangrak. The taxi outside will know where it is as it is very popular with foreigners.
Khet Bangrak Registration Office
5 Nares Road , Kwang Siphraya, Bangkok 10500
NOTE: If you are wanting to get a prenuptial agreement you need to do this before you register the marriage.
NOTE: If you are applying for a US Spouse Visa then have the marriage certificates translated