To get a work permit in Thailand, you need an employer who hires you. That can be any Thai Company like a Hotel, Dive Center or maybe even the government as an English Teacher. Even your Thai wife might be your employer and get a Work Permit for you if you want to run a smaller business.
To get a work permit for a foreigner, the company (Co.ltd) who wants to employ a foreigner needs a registered capital of at least 2 Million Baht for every work permit. So 4 Mill. for 2, 6 Mill. for 3 and so on. Further more it needs to employ at least 4 Thais for every foreigner they want to employ.
However, the employer can also be your “own company”, which hires you usually as a “Managing Director”
To apply for a work permit you’ll have to bring a huge amount of papers to the labor office. That includes copies of every page of your passport with a Non Im “B” Visa, a map that locates your working place, a hierarchy of the company, all company papers with all shareholders and all their ID copies, photos, application form, proof of your qualification for this job and a letter stating why you should make this job and not a Thai citizen.
However, at the Labour Office you will receive a list of all documents you’ll have to provide.
If you apply for a job and you don’t have a Non Im “B” Visa yet, you must bring all other papers to the labor office and they will issue a “WP3” form, which you have to take to a Thai Embassy in one of the neighboring countries to apply for a Non Immigrant Visa, Class “B”. Usually with one entry only.
After the new regulations the embassy you will only issue a 3-month Visa with only 1 entry, stating that you’ll have to show your work permit next time you apply for a Visa.
Workpermits are now issued always for 1 Year, independently of the validation of your visa. This makes it a little easier. Some years ago you had to extend your workpermit always together with your Business Visa.
Note: In Thailand, especially in the tourist centers you can find a number of law offices which are specialized on setting up companies for foreigners and handling the application for workpermits. You have to pay for it, however.