Recently someone asked me how they could go about staying in Thailand for 2-3 years. That's quite an involved question so I decided to publish my response here.
All of this is accurate as far as I know. The regulations change periodically so you should make sure to double check everything I've said here, especially if it's important to you. Actually, as a rule, when it comes to visas you should double check everything anyone tells you.
First up, what happens if you just show up? Currently if you arrive by air you get 30 days. If you arrive by sea or land you get 14 days. For people on these visas "visa runs" are a big part of their life. A visa run consists of travelling to the nearest border, typically Myanmar, Laos, Malaysia or Cambodia. You exit Thailand only to immediately re-enter the country getting you another tourist visa.
Although there is occasionally tough talk about clamping down on people staying in Thailand on back to back tourist visas I haven't heard of anyone actually being denied another one. Even when they reappear at immigration yet again with a passport full of Thailand tourist visas. That's doesn't mean it's a good idea to rely on getting yet another tourist visa. It's probably a good idea to have a little holiday in another country now and then if you have the means. Personally we recommend Laos or Malaysia.
Ok, so what if you want to do this properly and actually sort out something long term?
You can pre-arrange longer tourist visas. You're probably still only looking at maybe 3 months. The embassy or consulate that you are speaking to has a degree of discretion. We have found the Brisbane consulate in Australia to be particularly easy to deal with if you are in Australia. Straight answers, short turn around times etc.
If you are undergoing any sort of medical procedure in Thailand such as giving birth or having surgery you should be able to get a visa in the 3 to 6 month range depending on what you are having done. I'm not suggesting that you get surgery just to get a longer visa but if you are travelling there for medical treatment they will accommodate you with a longer visa.
Nips and tucks aside, the easiest option is definitely a retirement visa, also known as a non-immigrant O-A visa. If you're 50 or over, have no criminal record, have some money in the bank and don't need to work in Thailand this is likely the easiest option. You get 12 months although you have to report to immigration every 90 days. If you leave Thailand you have to apply for a re-entry permit before you depart Thailand or your 12 month visa will be cancelled. As you approach the end of your 12 months you can apply to get another 12 as long as you continue to be retired (and have money).
Not 50 or over? Me neither. What other options are available?
One of the easier visas to get a B visa. That's a non-immigrant B visa, a business visa. The name is a little misleading as you don't need a business to get one of these. The easiest way to get one is to enrol in a TEFL course somewhere like SEE TEFL in Chiang Mai while you are still in your home country. The school will assist you in arranging a B visa.
Once you have a B visa you get 12 months in Thailand. Oddly, one of the conditions of this visa is that you still have to do a visa run every 3 months. What you effectively have is a visa that grants you four 90 day stays. It's a little inconvenient but certainly better than having to do it every 14 days.
If you do do a TEFL course you would not be the first person ever to have completed the 4 week course only to then spend the remainder of the 12 months unemployed.
If you do go out and get a teaching job it should come with a work permit. That may not arrive until you have been working for several months. During that time you will inevitably have to do at least one more visa run to keep your B visa active. Once you have the work permit you trade visits to the border for visits to the local immigration office. Still inconvenient but a trip to immigration takes only a few hours while a visa run takes a whole day.
A word of warning about work permits. Your B visa can co-exist with your work permit. If you keep doing the 3 monthly visa runs you'll keep your B visa active. If you stop doing them your B visa will be cancelled and all you'll have is your work permit. If you then quit or get fired you can find yourself having to leave the country pretty much immediately. Some people elect to do the visa runs AND the trips to immigration to keep their B visa going. That way they are not so dependent on staying in their employer's good graces.
As an alternative to being a teacher, you could be a student. Education/student visas, known as ED visas, are apparently not hard to come by although I don't think I know anyone personally who has gone this route. You apply for a programme of study. University courses, Thai languages courses and apparently even Muay Thai training are all eligible. Once you have a formal letter of acceptance printed on the school's letterhead you can apply for the visa. Once you have the visa you can travel to Thailand. You then check in at your school and they will give you paperwork, a receipt for tuition paid etc, to take to immigration. Immigration will then extend your visa for up to 12 months depending on the length of the course you are undertaking.
While this may not initially be the most enticing option don't rule it out immediately. If you can find a course in something that interests you it may not be a bad idea. You're likely to find the tuition quite affordable depending on where in the world you are from. The time commitment is also likely to be much less than a full time job.
Be warned that you do actually have to go to class. Many schools report students who don't turn up to class to immigration. You may not find out that this has happened until you try to leave Thailand, discover that your student visa was cancelled months ago, that you have effectively been staying illegally in Thailand since then and now have a big fine to pay.
There are spouse visas available, also known as a non-immigrant O visa (Thai spouse). One of these gets you 12 months in Thailand. You can renew as long as you remain married. There are also financial requirements you must be able to meet. I'm not going to talk a lot about these. If you are already engaged or married to a Thai citizen look into it. If you are considering getting married just to get a visa, find another way.
That's pretty much all of your options. Tourist visas and visa runs, a B visa then possibly a work permit, an ED visa. None of these are the outright best easiest way for a 2 to 3 year stay. Regardless of whether you get a B visa then a work permit, two years worth of ED visas, a B visa then an ED visa or some other permutation there will be complications, paperwork and aggravation. Foreigners living in Thailand have to learn how to work within the system, how to deal with the bureaucracy and how to patch together a solution that works for them.