Will my Non-B visa be cancelled when my work permit is cancelled, and how can I convert it to a spouse visa in Thailand?

As BOI they will do cancellation both of your extension and WP at One Stop Service at Chumchuri Square (if in Bangkok). But you need to go to immigration office in Chaengwattana for your extension based on marriage..

Likely they will give you 7 to 21 days to leave the country, but this is not extension anymore. Not all the immigration office let you apply another extension during this no-more-extension period. Someone couldn't do in Bangkok to change the reason for extension within this period.

If you want to get extension for different reason, better not get those grace days and need to go to immigration office same day on your cancellation or earlier if your employer can arrange those in advance.

I did this 3 years ago from non-b to non-o based on marriage, although not BOI my company was under the one stop service at Charmchuri Square. I actually used the agent/lawyer that my company was using to do the process and paid them personally to handle the switch. You can do it yourself but you will spend quite a bit of time. if you have more important things to do, any law firm dealing with visas will be able to handle it for you, just have to find one that doesn't charge too much 😁

When my WP was cancelled some 6 years ago now, I went to immigration the next day to change from Non Imm B to O on retirement. I had a warning so all my documents were correct. Nevertheless I was charged 2 days ov erstay - the day my WP was cancelled and the next day when I went to Imm. Go figure! Just a heads up.

If you have all the documents supplied by the BOI office, you should contact them directly as they have some special agreements and can help you to apply for other visa.

Do you have an extension of stay?