I'm married to a Thai, have a visa based on marriage, and am a shareholder in a family company. I don't work for the company but share the profits. Am I supposed to have a work permit?

More chance of getting an answer in the Visa Forum.

Moved.

Only holding shares does not constitute working, as long as you don't sign any contracts etc it is just an investment.

Thanks

In a case like this, is it possible to use the income gained from being a shareholder for the income requirement for the extension of stay based on marriage?

That should be the case, you should proof the income with tax documents.