What are the documentation and requirements for converting a 3-month Non-O spouse visa to a 1-year visa in Thailand?

The biggest requirement is that you have at least bt400,000 in a Thai bank account in your name only for at least two full months before you apply. The other documents that can take time to get if you rent is a copy of your lease, a copy of the actual owner's Thai ID card, and a copy of the house book he is listed in. Then one set of your original marriage certificate, and local Amphur registration certificate. You should have gotten two sets of these when you were legally married. The following years you only need copies, but you do need to show them the originals. A copy of your Thai wife's ID card, and a copy of the house book she is listed in. Two letters from your Thai bank, one stating the account is your only, and the other showing your deposits for at least the last two months showing your bt400,000 balances for those months before you apply, and it doesn't matter where it comes from just that it is in your account. Copies of the data page of your bank book, and last pages showing your balance for at least the last two months. Copies of your passport pages. I always give them copies of every page in my passport, then there is no question of which ones they actually want, as it has changed from year to year. Pictures of you and your wife in front of your rental showing the address, picture of both of you at the entrance to the building you are in if applicable, a picture in front of your apartment entrance of both of you and that shows clearly the room number, if there is one. Then at least two pictures of both of you together inside your living quarters. The last thing is a hand drawn map of how to get to where you live from the closest main street. Some offices allow a Google map printout, but not many. Those are the basics needed, although some want more. If you are using the main immigration offices, division 1, then you only need one copy of everything. If you are not using the main offices, then you need at least two sets of copies, as one has to be sent to the Bangkok main office.

Keep copies of everything, as for the following years, if you don't move, all you need to update are the pictures, and your bank letters. All the rest is the same copies. Oh, and you need a current passport photo. Don't try to use pictures from past years as they are all scanned into the computer, and checked to make sure you are providing new pictures. This is my experience for the last seven times extending my type O extension based on Thai wife. After your application is accepted you have an under consideration period before your passport is stamped with your new extension. This gives them time to check out where you both live together, to make sure it is a legitimate marriage, and they can also ask your neighbors, before they actually give you your extension stamp. If what they find does not convince them you do live together, they can deny your extension. The other thing is anytime you go to immigration concerning your marriage extension always bring your wife, or they will not talk to you at all, or let you apply for anything concerning your extension.

Every office has their own requirements. Here is a general guideline.

You should go to your immigration office and ask for their checklist.