When you decide to retire in Thailand you would need to obtain a Thailand Retirement Visa or Thai O-A visa. This will allow you to retire in Thailand and the visa would only be needed to be extended once a year in Thailand. The Thailand Retirement Visa is normally obtained in country. The procedure used by most Westerners when they retire in Thailand is to obtain a Thai Visa "O". This Thai Visa is usually called the Thai marriage visa, however it is a general visa which covers what the other don't. "O" stands for "Other" giving it a broad application.
If you are over the age of 50 at the date of application, you can apply for a Thai retirement visa. You need the following documents when you apply for the visa at the Thai embassy in your country.
The application process when it starts is very easy but it is the extension in Thailand that takes almost a month to complete and also the documents needed are much more complex. The following documents are needed for the extension. Note that if you have a Thai wife the marriage visa is less of a problem to obtain as it requires less documentation. Most expats in Thailand who are married opt for the marriage visa and not the retirement visa.
If you have completed the above as stated it takes about 4 weeks to complete the process in Thailand. Also note that once granted you have 6 months to bring your household items into Thailand. Normally the attorney who does your application will also provide you with assistance with Thai Customs when your goods arrive in Thailand. See Household Items in Thailand for more details about the process of bringing your goods in Thailand once you have a retirement visa.
Retirees who are married to a foreigner as an example an Australian who is married to say a Filipino can apply for his "O" status non immigrant visa under the normal criteria of 800,000 baht or 65,000 baht coming in each month. However if he /she wants to include spouse on this Visa he/she must show evidence of marriage, such as a marriage certificate.