Can I change my ED Plus Job Search visa to a Non-B visa without leaving Thailand?

Theory says yes. Practice says that very few employers can (or will) provide the extensive paperwork necessary.

You’d probably find that most would prefer you to exit and obtain a Non B outside of the country

Sounds complex procedure

Based on the current regulations, it may be possible to convert from an ED Plus (Job Search Extension) to a Non-Immigrant B visa without leaving Thailand, provided you meet the eligibility requirements and Thai Immigration approves the application.

Generally, you’ll need a valid permission to stay, a confirmed job offer, and your employer must provide the required supporting documents. The application should also be submitted before your current permission expires.

That said, the practice can vary between Immigration offices, and some employers may still ask employees to obtain a Non-B visa from a Thai embassy or consulate outside Thailand.

It would be best to check directly with your local Immigration Office or ask your employer’s HR, as they will know the procedure that applies to your specific case.