Is it possible to obtain a Marriage Visa Extension based on income if employed by a foreign company?

After your extension is inked in, you can withdraw the 400K, it only needs to be in the bank for the 2 months before you apply for an extension.

The way that works is you'd have to transfer in to the country a minimum of 40K baht a month, each month, every month for the previous 12 months before you apply for the next extension using monthly income method.

You need to check with your immigration office though, because while there is no rule saying you can't use monthly income method for marriage extension while working abroad, SOME offices will only let people do it if they legally work for a thai company (work permit etc)

Definitely check to see with your office well before you decide to show up and get the extension, because IF they say you can't do it and need to show banked money that 400K would have to be in the bank for 2 months before you apply for the next extension