Affidavit of Foreign Law. When a Thai court or administrative authority must apply or recognize rules from another country, those foreign rules are a question of fact that must be proved — and an affidavit of foreign law is the standard, efficient way to do it. This article explains when you need one, who should prepare it, exactly what it must contain, the required authentication and translation steps, courtroom practice (including cross-examination), timing and costs, and a practical checklist to ensure admissibility and persuasive force in Thailand.
What it is and why Thai courts require it
An affidavit of foreign law is a sworn, written statement by a qualified expert that sets out the content, sources and application of a rule from another jurisdiction (statute, case law, practice or public-law rule). Under Thailand’s private international law practice and procedural rules, when parties ask a Thai court to apply foreign law the party relying on that law bears the burden of proof — the court will only apply foreign law if it is proved to its satisfaction. In practice, Thai judges expect a focused, sourced, sworn expert statement rather than broad academic commentary.
When you need an affidavit of foreign law
Typical situations include:
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cases where substantive law chosen by the parties is foreign (contract law, property law, succession rules);
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recognition/enforcement issues (validity of a foreign judgment, effect of a foreign notarial act);
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family-law matters (validity of a foreign marriage/divorce); and
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probate or company law questions where the foreign formation/registration rules are material. In short: when the outcome depends on what the foreign rule actually says and how it operates.
Who should prepare and swear the affidavit
Best practice: instruct a qualified expert from the foreign jurisdiction — typically a lawyer admitted there, an academic specialist, or a high-level practitioner with demonstrable expertise. The deponent must identify credentials (bar number, academic posts, publications), explain instructions received, and swear the affidavit before a competent officer in the foreign country (notary, commissioner). Thai courts give greater weight to a direct expert affidavit than to a local counsel’s summary of foreign law. Specialist Thai firms also assist in coordinating experts and legalization.
Required content and structure (practical template)
A persuasive affidavit should be clear, numbered and exhibit-driven:
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Deponent identity & CV — name, practicing jurisdiction, qualifications, experience relevant to the issue.
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Instructions & scope — who instructed the expert and the precise legal questions posed (e.g., “Whether under X law a foreign divorce obtained on Y date is valid for purposes of marriage capacity?”). Narrow questions are more useful than broad essays.
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Date-cutoff — state the date as at which the law is being reported (e.g., “law of X as at 1 Jan 2025”).
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Materials relied upon — list statutes, cases and official sources; annex primary sources (statutes, case reports) as exhibits.
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Statement of law — precise, sourced propositions linked to authorities.
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Application to facts — reasoned application to the material facts the Thai court must decide.
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Conclusion — concise answers to the numbered questions.
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Oath & notarization — sworn declaration with date, place and proper notarization details. Courts prefer numbered, exhibit-indexed bundles to speed review.
Authentication, translation and the legalization chain
Affidavits executed overseas normally require authentication to be admissible in Thailand. The typical chain is:
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sworn/notarized in the foreign state;
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authenticated by the foreign state’s competent authority (or apostille where applicable);
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consular/legalization by the Royal Thai Embassy/Consulate where required; and
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final legalization by the Thai Ministry of Foreign Affairs (MFA) if the receiving Thai office requests it.
If the affidavit or exhibits are not in Thai (or English in some MFA cases), provide certified Thai translations; translations may also need notarization and legalization. The MFA publishes procedural guidance and offices that handle legalization submissions. Failing to follow the exact chain is the most common documentary reason for rejection.
Evidence strategy & exhibits — what convinces judges
Courts expect primary authorities (statutes, official case reports) annexed in full, not just secondary commentary. Where you rely on administrative practice, attach official circulars, practice notes or government web pages. Provide a concise exhibit index and translations aligned to the affidavit paragraphs (e.g., “Exhibit A — statute X, English translation, pp.1–12”). Good exhibit management reduces judicial requests for supplementation.
Courtroom practice: cross-examination and expert attendance
Affidavits are written evidence, but Thai judges commonly reserve the right to require oral examination of the expert if the foreign law is contested or central to the case. That means you should: obtain the expert’s advance agreement on availability (remote or in-person), budget for attendance fees, and ensure the expert can be produced for examination at short notice. If attendance is impractical, set out in the affidavit the expert’s willingness to appear by video and provide contact details.
Timing, costs and practical timeline
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Preparation time: narrow, focused questions with easily available authorities — several days. Complex multi-jurisdictional research, translations and legalization — several weeks.
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Costs: expert fees (research + drafting + attendance), translation and notarization, apostille/consular/legalization fees, and courier/consular service charges. Cross-border coordination (multiple experts, multi-language bundles) increases cost materially. Plan and budget early.
Common pitfalls (and how to avoid them)
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Vague scope: an affidavit answering overly broad questions invites rejection — keep questions tight.
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Missing primary sources: don’t rely only on textbooks—attach statutes and cases.
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Incorrect legalization chain: check MFA/embassy rules for your country early.
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Unwilling expert: secure the expert’s agreement to attend for possible examination before drafting.
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Poor translations: use certified translators and label translations with exhibit links.
Practical checklist (ready to use)
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Clear written instructions and the precise legal questions.
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Factual statement bundle the expert can assume.
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Proposed expert CV & confirmation of availability for hearing attendance.
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Annex list of primary authorities (statutes, cases) to be attached.
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Notarization, apostille/consular step plan, and MFA legalization path checked for the expert’s country.
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Certified Thai translations of affidavit and exhibits with exhibit index.
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Budget for expert fees, translations and legalization fees.
Conclusion
An affidavit of foreign law is a technical, high-value piece of evidence in Thai cross-border matters. Its admissibility and persuasive force rest on (1) the expert’s credentials, (2) meticulous citation and annexing of primary authorities, (3) correct notarization/legalization and certified translation, and (4) advance planning for possible expert examination. Start early, narrow the legal questions, coordinate the legalization chain with Thai counsel, and prepare a tight exhibit bundle — those steps convert an affidavit from a formality into decisive, court-worthy proof.
