I'm about to send in the application for a type-O visa so that i can come to thailand and get married (with thai citizen) and then apply for 1 year extension.

Is it ok to put this as the "Purpose of Visit" on the application?

Also it says:

"Non-immigrant visa applicant must submit an invitation letter/proofs from persons/institutions concerned stating the purpose of visit and the length of stay."

So i should have my fiance write a letter saying that i am coming to get married and stay indefinately?

Getting married is not normally a valid reason for a non immigrant visa so it will depend on the Consulate. A letter from her may well help as it gives them something for the "file". In any case the non immigrant visa only allows a 90 day stay so you should probably not indicate longer than that in the length block. FYI: you do not need a non immigrant visa to get married. Once married they can be easily obtained. One year extensions are a bit harder.

So it would be ok to go on a tourist visa, then get married and upgrade to a 3 month type O, then upgrade again to the 1 year extension?

That will work. But if you have access to an honorary or official Consulate that will issue you the O visa it would make sense to take advantage of it.

So it would be ok to go on a tourist visa, then get married and upgrade to a 3 month type O, then upgrade again to the 1 year extension?

That’s right.

1. Get a tourist visa.

2. Enter Thailand with the tourist visa (i.e. be sure to enter the visa information on the Thai arrival card)

3. Get married.

4. Go to nearest immigration office, with marriage certificate and wife, and change your tourist visa to non-O visa for the reason of supporting Thai wife.

5. Get annual extension for the reason of supporting Thai wife.

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Maestro

Make sure you bring all the necesary documents with you,

as it takes a few days to get them all translated and notorised before

you get married, and it is surprising how the time can run away when you

are having fun as well!!

Good luck