What happens to my non immigrant visa when I renew my expired passport in Thailand?

Yes, you receive a new passport without any stamps inside. If you still use the original visa and doing border runs every 90 days, you take both passports, the old one to show the visa, the new one to collect the stamps. If you have a big stamp from Immigration Office with in the second line Extension of Stay permitted up to ../../.. , then you visit the Immigration Office to transfer this stamp into your new passport Difference between a visa (sticker which can not be transferred to new passport) and the Extension of Stay which must be transferred to new passport.

Once you have your new passport you will need to go to your immigration office win your Provence and have the visa moved to the new passport.