I entered Thailand on a Non-O visa a couple of weeks ago. I will be applying for an extension of stay on Marriage grounds. A prospective employer wants to apply for a work permit for me. My question is, can a work permit application and an extension application on marriage grounds run at the same time or must I obtain the extension before the work permit application is made ?

I am sure someone wiser will be along shortly, but would guess it wouldnt matter...which way you are doing as you are not changing visa types per se

Applying for a work permit and applying for an extension of stay are not interrelated processes. Labor Department and Immigration will go about their own business without regard to the other department. Plenty of posters on ThaiVisa report having a work permit along with a marriage extension of stay. The only visa requirement in the rules for getting a work permit is that it must be a non-immigrant type, not tourist or transit. Some local labor offices have been known to ask for a non-immigrant "B" visa.

As said, the two processes work independently of each other. At the time your work permit is issued you must be in possession of either a valid Non-Immigrant visa that supports working (NonO or NonB) or extension of stay based on marriage.

Many thanks for your assistance.