Can I apply for a marriage visa now while on a tourist visa in Thailand?

@Jack ***************

be very aware that for the type O visa extension based on Thai wife it doesn't matter where the money came from. The requirement that it comes from overseas is only relevant for a retirement extension, not a marriage extension. Also, whenever you go to immigration concerning your marriage visa extension always take your wife with you, as most offices will not do anything if your wife is not with you.

you should have applied very soon after you entered. In order to be allowed to apply for the "change of visa type" from the Tourist Visa to the "90-days Non-Imm-o marriage visa", you need to have a minimum of 15 working days left on your stay permit stamp. Because the "90-days Non-Imm-O Visa" will be issued for "14 days under consideration". On the day of your application to the change", you need to show a minimum of 400,000.- THB in your Thai bank account, with a proof that they have been transferred from abroad, there is no seasoning needed at this point however. Normally most applicants do not wait until they fetch their 30-days extension on top of the 60 days stay permit from the tourist visa, they don't even wait so much longer into the first 60 days, than what time they need to open a bank account on a tourist visa - for which they might need the help of an agent.

You can apply now if you have 400k in a Thai bank account

It doesn't matter. You just need to have a minimum number of days left to apply. Between 14-21 depending on the office.