An affidavit of foreign law (also called an expert statement on foreign law) is a sworn, written statement prepared to explain the content, scope, and application of a foreign legal rule to a court or administrative body. In cross-border litigation, probate, family law, or regulatory proceedings that touch on rights or legal acts governed by another country, Thai courts and authorities often need an authoritative statement about that foreign law so they can decide how to apply it. Siam Legal and other Thailand-based law firms routinely prepare these affidavits because Thai judges and officials are frequently unfamiliar with foreign legal systems.
When an affidavit of foreign law is required
Thai proceedings may require proof of foreign law when a case raises issues such as the validity of a foreign marriage or divorce, the content of foreign corporate law for a cross-border contract, recognition of foreign judgments, or the proper administration of property under foreign succession rules. Where a foreign statute, foreign court decision, or a foreign notarial act is material to an issue, the foreign rule must be proved — and an affidavit of foreign law is a common, efficient way to do so. Courts that lack personal knowledge of the foreign system rely on the affidavit to fill this gap.
Who may prepare and swear the affidavit
There are two common approaches:
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Qualified legal experts (foreign lawyers, academics, or lawyers admitted in the foreign jurisdiction) prepare a sworn statement explaining the foreign rule and how it applies to the facts. These statements are often notarized or sworn before an authorized officer of the foreign jurisdiction.
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Local counsel (Thai lawyers) may prepare a translation and an explanatory affidavit that sets out the foreign law as reported by an expert, attaching the expert’s statement as evidence. Because courts prefer primary expert statements, direct affidavits from the foreign expert are typically stronger.
Where the affidavit is sworn abroad, it will usually require local notarization and consular/embassy authentication before being presented in Thailand (see “legalization” below). Siam Legal and similar firms often coordinate the foreign expert statement, notarization, and subsequent legalization steps.
Content and form: what the affidavit should contain
A useful affidavit of foreign law should be precise, sourced, and practical:
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Identity and qualifications of the deponent: full name, address, title, professional qualifications, license number, and a short CV demonstrating competence to opine on that area of foreign law.
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Scope and question(s): a clear statement of the legal question(s) the affidavit answers (e.g., “Under English law, a deed executed in X circumstances is valid if…”).
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Statement of law: concise statement of the governing statute(s), relevant case law, and commentary explaining how the law applies to the material facts. Cite specific statutes and cases (with paragraph or section references where possible).
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Evidence basis: attach copies of primary sources (statutes, case reports), secondary sources relied upon, and translations if necessary.
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Opinion and conclusion: a reasoned conclusion that directly answers the legal question posed.
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Oath / notarization clause: a sworn declaration, date, signature, and place; the affidavit should be sworn before a notary or authorized official.
Courts will discount vague or unsourced opinions; the more the affidavit points to primary authority in the foreign jurisdiction, the stronger it will be.
Authentication and admissibility in Thailand
Documents sworn or notarized abroad generally must be authenticated (legalized) to be admitted in Thailand. Typical steps include notarization in the country where the affidavit is sworn, embassy/consular certification by the Thai embassy (if required by the receiving Thai office), and final legalization at the Thai Ministry of Foreign Affairs (MFA). Because Thailand’s approach to apostilles and consular legalization varies by country and purpose, practitioners frequently verify the exact chain of authentication with the MFA or the receiving Thai authority in advance. These legalization steps ensure Thai courts and administrative bodies will accept the affidavit as evidence.
If the affidavit is in a foreign language, it must be translated into Thai by a certified translator; courts usually expect translations to be certified and — in some cases — notarized before legalization. Siam Legal’s materials and procedural write-ups confirm that Thai courts require documentary and testimonial evidence in Thai, or translated and certified equivalents.
Practical differences: affidavit vs. expert oral testimony
An affidavit is a written record and often sufficient, but courts may still call for cross-examination or oral expert testimony if the matter is complex or disputed. Where the opposing party challenges the accuracy of the foreign law as stated, the court may require the expert to attend (in person or remotely) for examination. For this reason, the affidavit should anticipate likely challenges and set out supporting authorities fully so that the court can assess the expert’s reasoning without needing immediate oral proof.
Typical workflow and timing
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Identify the legal questions the Thai court needs answered.
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Retain a competent foreign expert and instruct them precisely on questions and required format.
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Draft the affidavit with the expert; include annexed sources and translations.
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Notarize / swear the affidavit in the foreign jurisdiction.
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Authenticate / legalize via embassy/consulate and MFA if required.
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File and serve the affidavit in the Thai proceedings, ensuring translations are certified and attached.
Timing depends on the foreign expert’s availability and the speed of legalization steps across jurisdictions — expect anything from a week (where fast service is available) to several weeks for complex or multi-jurisdictional verification.
Common pitfalls and how to avoid them
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Insufficient sourcing: Avoid affidavits that make unsupported assertions; cite statutes and cases.
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Weak expert credentials: Courts scrutinize the deponent’s expertise — choose a qualified practitioner or academic.
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Authentication errors: Follow the MFA and embassy requirements exactly; a missing consular stamp or incorrect form can invalidate admission. Consult the Thai MFA legalization guidance early.
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Translation mismatches: Ensure English ⇄ Thai transliteration and legal terminology match official documents (names, dates, case titles).
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Failure to anticipate cross-examination: Be prepared to produce the expert for examination; set expectations contractually with the expert about attendance and fees.
Use beyond courts: administrative and consular contexts
Affidavits of foreign law are not limited to litigation. Administrative agencies, regulatory bodies, embassies, and land offices often need authoritative explanation of foreign legal effects (e.g., for admitting a foreign power of attorney, recognizing foreign marital status, or validating a foreign company’s documents). Preparing the affidavit in a format suitable for both courts and administrative use reduces duplication and speeds processing. Siam Legal and other service providers commonly market affidavits for both court and administrative needs.
Conclusion
An affidavit of foreign law is a technical but essential documentary device in cross-border matters in Thailand. Its effectiveness depends on the deponent’s qualifications, the clarity and sourcing of the opinion, and strict compliance with notarization and legalization rules so Thai authorities will admit it. Early planning — identifying the precise legal question, selecting the right expert, and mapping the necessary authentication chain (notarization → embassy → MFA) — reduces the risk of delay or rejection. When in doubt, instruct experienced counsel to coordinate the expert statement, translations, and legalization steps to ensure the affidavit will serve its evidentiary purpose in Thailand.