TL;DR:Register the marriage at the Amphur with proper documents, then apply for a Non-Immigrant O marriage visa (financial proof required); work needs a separate permit and children of a Thai parent are automatically Thai citizens.
To marry a Thai national you must register the marriage at the local district office (Amphur) — a ceremonial wedding alone is not legally binding. The Thai spouse brings ID and Tabien Baan (house registration); the foreigner needs passport, arrival card and an embassy-issued Affirmation/Certificate of Freedom to Marry, translated and legalized by the Thai Ministry of Foreign Affairs. Once registered you can apply for a Non-Immigrant O (marriage) visa and extend it in Thailand; the usual financial qualifying options are 400,000 THB in a Thai bank (held 3 months) or monthly income of 40,000 THB, plus evidence of cohabitation and your spouse’s ID/Tabien Baan. Employment requires a separate work permit from the Ministry of Labour. Registering the foreign spouse on the Tabien Baan simplifies many procedures. Children with one Thai parent are Thai citizens by birth. For official forms and latest details, check the Thai Immigration Bureau and the Thai Ministry of Foreign Affairs websites.
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