Affidavit of Foreign Law

An affidavit of foreign law is a sworn, written statement by a qualified expert that explains the content, interpretation and application of a foreign legal rule for the benefit of a Thai court, tribunal, administrative body or registry. Because Thai courts do not take judicial notice of foreign statutes, case law or administrative practice, proof of foreign law is treated as a question of fact. For any cross-border dispute or transaction where foreign law determines rights (family law, validity of foreign marriages/divorces, corporate formation rules, insolvency effects, foreign succession, foreign public registers), a correctly prepared affidavit of foreign law is often essential.

This guide explains when you need one, who should prepare it, how it should be structured, authentication and translation steps, practical drafting tips, likely procedural uses in Thailand, common pitfalls, and a concise checklist for clients and counsel.

When you need an affidavit of foreign law

Thai proceedings ask for foreign-law proof when:

The validity, existence or effect of a foreign legal act is material (e.g., whether a foreign divorce dissolved a marriage).
Foreign substantive law governs a contract or proprietary right (choice-of-law clauses).
Recognition or enforcement of foreign judgments, company records or notarial acts is at issue.
Administrative or consular proceedings require an expert explanation of foreign requirements.

If the legal effect of the foreign rule will change the case outcome, assume you must prove the rule — and do so early in your evidence plan.

Who should prepare and swear the affidavit

Best practice calls for a qualified expert from the foreign jurisdiction:

A lawyer admitted in the foreign jurisdiction with relevant practice experience, or
An academic specialist who publishes in the field, or
A senior official or recognized practitioner with documented expertise.

The expert must set out their qualifications (bar number, position, publications), confirm they were instructed by counsel, and swear the statement before a competent officer (notary, commissioner for oaths, magistrate) in that foreign jurisdiction. Where local practice prefers, Thai counsel may prepare a supporting affidavit that summarizes the expert evidence and attaches the expert’s sworn statement as an exhibit; but courts generally prefer the expert’s direct sworn statement where possible.

Core structure and content (must-have elements)

A robust affidavit of foreign law follows a clear, numbered structure so the judge can find and verify authorities quickly. Typical elements:

Title and identification of the deponent — full name, contact, professional role, admission details, short CV and an explicit statement of the deponent’s competence to give the opinion.
Instructions and scope — description of who instructed the expert, the narrow legal questions posed, and the date or point in time the law is reported (e.g., “law of England & Wales as at 1 January 2025”).
Materials relied on — list primary sources (statutes, regulations, cases) and secondary materials relied upon; attach copies as exhibits (label Exhibit A, B, etc.).
Statement of foreign law — precise, sourced statements of the law with statutory citations and case references (neutral citations, paragraph numbers). Explain any uncertainties or conflicts in authority.
Application to facts — a reasoned application of the stated law to the material facts of the Thai proceedings, answering the discrete legal questions posed.
Conclusion — short, numbered answers to each question.
Oath/attestation — sworn declaration, signature, date and notarization details.

Avoid conclusory assertions without authority. A persuasive affidavit ties conclusions to specific primary sources and explains why the authorities support the answer.

Authentication, translation and legalization chain

An affidavit sworn abroad will usually require authentication before Thai authorities accept it. Practical steps often include:

Notarization in the country where sworn (or affirmation before an authorized officer).
Apostille or foreign-ministry authentication, depending on whether the foreign state is a Hague Apostille Convention signatory and the receiving requirement.
Consular certification (Thai Embassy/Consulate) where required by the Thai receiving office.
Legalization at the Thai Ministry of Foreign Affairs (MFA) if the Thai office requires final authentication.

If the affidavit or exhibits are not in Thai, provide a certified Thai translation, and where required have the translation notarized and legalized in the same chain. Map the precise chain with the Thai counsel early — a missing consular stamp or incorrect notarization is a common cause of rejection.

Evidence strategy and attachments

Annex primary sources: statutes, official practice directions and full texts of cited cases (not merely citations).
Provide translations of statutes and cases (certified).
Attach an exhibit index: short table of exhibits with description and exhibit page ranges.
Supply contemporaneous documents used to show practice (official guidance, government forms) when the expert refers to administrative procedures.

A well-organized bundle speeds judicial review and reduces requests for further proof.

Practical drafting tips

Narrow the questions: broader opinions invite challenge and increase cost.
Date the law: state the cut-off date for legal materials and whether any intervening changes are noted.
Anticipate counter-arguments: address obvious contrary authorities and explain why they do not change the conclusion.
Neutral tone: write analytically, not advocacy-style. Judges weigh objectivity.
Provide contact details for the expert and confirm availability for remote or in-person examination if the court requires cross-examination.

Courtroom and procedural realities in Thailand

Thai courts may require the expert’s attendance (in person or by video) if the opposing party disputes the affidavit. Confirm attendance terms and fees in advance.
Expect judges to verify translations and exhibit authenticity; a deficiency may prompt rejection or require supplementary affidavits.
When foreign law is central to relief, file the affidavit as early as possible so the court can consider it pre-trial.

Common pitfalls to avoid

Using an unqualified deponent: a lay statement or non-expert commentary is weak.
Poor exhibit management: missing primary sources or untranslated authorities undermine credibility.
Incorrect legalization chain: missing apostille/consular step.
Overbroad or vague scope: avoid general treatises that do not answer specific legal questions.
Not planning for cross-examination: experts unwilling or unreachable for hearing stage cause procedural headaches.

Cost, timing and resourcing

Timetable and cost depend on complexity. Narrow, focused questions with readily available authorities can be completed in days; complex issues requiring deep research, multiple jurisdictions or translations can take weeks and attract higher fees. Budget also for notarisation, apostille/consular/legalization fees and certified translations.

Client checklist before instructing an expert

Clear written instructions and a short statement of the legal questions.
A factual bundle describing the material facts the expert must assume.
Copies of any foreign documents requiring translation (marriage certificates, corporate records, judgments).
Desired cut-off date for legal materials.
Confirmation the expert will be available for possible testimony.
Budget authorization for legalization and translation steps.

Conclusion

An affidavit of foreign law is a technical, high-impact evidentiary tool in Thai cross-border matters. Its weight depends entirely on the expert’s credentials, meticulous citation of primary sources, correct notarization/legalization, certified translation and a tightly focused, reasoned application to the facts. Early planning with Thai counsel — choosing the right expert, narrowing the questions, and mapping the legalization and translation chain — transforms an affidavit from a box-ticking document into persuasive, admissible evidence that materially advances your case.