For foreign workers, the Foreign Working Act requires that all foreigners working in Thailand obtain a work permit (with a few exemptions). Besides the standard “work visa,” Thailand has also introduced new types of visas designed to provide more convenience to foreign workers. The differences between each type of visa are as follows:
Types of Work Visas in Thailand
Foreigners entering Thailand are not permitted to work, regardless of their types of visas, unless they are granted a work permit. Those who intend to work in Thailand must hold the correct type of visa to be eligible to apply for a work permit.
Source: https://www.boi.go.th/upload/content/Quick_Guide_to_Starting_a_Business_in_Thailand.pdf