Will my passport expiration affect my 1-year Non-Immigrant O visa application in December?

In December, when you extend your visa, they will only extend until July 17, the end of your passport validity.

Also, travel in April (with less than 6 months validity) will be impossible unless you’re only flying home. Most

Countries won’t let you enter their country without 6+ months on your passport.

Your biggest problem will be to get a Thai bankaccount, even when it is for Non-O.

I would get a new passport now, before applying for visa.

Correct wording is important!

*** in December you do not apply for a “one year Non-Immigrant O visa”.

The 90-days Non-Imm-O visa with which you are going to enter Thailand, will become invalid upon entry. You will receive a 90-days “stay permit”, based on this visa.

By December, you will then apply for a “one year extension of the stay permit”

*** You should apply for a new passport in your country ASAP!!

Immigration will issue the “1-year Extension of Stay” only for the rest of the time of your passport validity

*** and do not forget, on the same day when you get issued the “1-year Extension of Stay Permit” (EOS) stamp, buy a single re-entry permit for the extension. It costs 1000 THB and will keep your 1-year stay permit alive when you exit the country before the expiry of the EOS

Apply for a 1yr extension during December with a passport(validity of 7mths) is unwise and how are you going to use that(less then 3mths) to travel out of thailand?

You will be applying for a 1 year( well, till July) extension not a visa

With planned overseas travel which could conceivably, if not likely, require you to stay over past your passport's expiration date, you should renew your passport now.

Not an issue getting the extension, providing you meet all the criteria. However the extension will only be until July 17th unless you renew your passport prior to applying.