Can I convert my DTV to Non-B visa while in Thailand?

You cannot leave and return on visa exempt because you have a valid multiple entry visa. If you leave and return you'll just be stamped in on your DTV.

The law that created the DTV specifically says it can be converted to another visa type inside Thailand. You'll need to check with your local immigration office to find out details and their willingness to do so.

You need to leave and apply for a non b in Thai embassy. You work needs to give you the paperwork you apply non b 3 months when you come back your employer the applies for 9 month extension in Thailand local immagration followed by your work permit at labour dept

Better to check with immigrstions but I am assuming that you will need to change visas because they will be your legitimate reason for long stay. Some companies will do the application for a work visa and it will be pegged to the company while some may insist that the employee does all the process by themselves. But in most cases that I know, even if you have approval and a new visa from within the country, you will still need to do a border bounce to stamp out of the old visa and in with the new.

I was on an O with a multiple re-entry permit. To get a B I had to leave the country and get the B at an Embassy. As other have said. Ask immigration if they will convert in country.

DTV is issued by MFA, not immigration so it's a difficult one. Enquire first at immigration and see what they say. You might have to get the issuing embassy to cancel it

Better to ask to immigration office