The Verdict: Need More Info
This turns on whether civil registration shows you have lived in Thailand continuously. Take your household registration records to your district office (amphur), where the claim is made.
Announcement No. 337 of 13 December 1972 stripped nationality from many people born in Thailand to non-Thai parents, and blocked those born later. Section 23 of the Nationality Act (No.4) of 2008 reversed it, for them and their Thailand-born children, where continuous domicile is proven by civil registration and conduct is good. A family that left Thailand cannot meet that test.
A Cabinet Resolution of 29 October 2024 opened a faster pathway for about 335,000 long-term residents and members of recognised ethnic minorities (permanent residence) and over 142,000 of their Thailand-born children (nationality). Over 100,000 cases have been resolved, and an action plan for 2025 to 2027 was approved in March 2026.
Useful records are household registration (including coloured-card records for non-nationals), school records, and anything your parents or grandparents registered. If you belong to a recognised ethnic minority, say so.
UNHCR and local legal clinics, especially in the northern provinces, help with these cases free of charge.