I have recently received the 90 days permit stamp of my now expired Non-O multiple entry visa and am hoping to receive a re-entry stamp for this 90 days stamp at Suv airport prior to departure for a few weeks visit to my home country (Europe) on the coming weeks. I am planning to get a new passport there, as my old one has less than 18 months validity, preventing issuance of new Multi Non-O, which I would like to apply for later at SEA country. Will I be let onboard my flight back to Thailand and in by immigration with the re-entry permit in the old, at that time cancelled passport and new blank passport? I will show them both? Grateful for any advice/experience on this issue. Will my plan work out? Thanks!

You can get a re-entry permit that will keep the remainder of the 90 days valid when you re-enter the county.

The re-entry permit will remain valid in your old passport. Just show both passports on entry to use the re-entry permit in the old one.

Yes.

Might be me, but where did the eighteen months validity requirement come from? Should be six, I'm sure.

1 minute ago, Jonmarleesco said:

Might be me, but where did the eighteen months validity requirement come from? Should be six, I'm sure.

For a single entry non-o it is 6 months. For a multiple entry non-o visa it is 18 months but some embassies and consulates will do it with one year of passport validity.

From MFA website for  non immigrant visas. http://www.mfa.go.th/main/en/services/4908/15398-Issuance-of-Visa.html

Quote

Passport or travel document with validity not less than 6 months. The validity of 18 months is required for one year visa application.