What this guide covers
Witness statements are the foundation of factual evidence in international arbitration. A well-drafted witness statement frames the factual narrative, pre-empts cross-examination challenges, and saves hearing time. Poor witness statements waste tribunal time, invite adverse inference, and damage credibility.
IBA Rules on the Taking of Evidence — the standard framework
The IBA Rules on the Taking of Evidence in International Arbitration (2020) are the standard reference for evidence procedure in international arbitration, including DIAC, SIAC, and arbitrateAD proceedings. While not automatically incorporated, tribunals routinely adopt the IBA Rules or use them as guidance. Under the IBA Rules: witness statements are submitted in writing before the hearing (Art 4); the witness attends the hearing for cross-examination; the witness may be excused from cross-examination by agreement or tribunal order.
IBA Rules Art 4.5 sets out the required content of a witness statement: (i) the witness's full name and address; (ii) the witness's present and past relationship with any of the parties; (iii) a description of the witness's background, qualifications, training, and experience where relevant; (iv) a statement of the facts and circumstances supporting the party's case; (v) a confirmation of the accuracy and completeness of the statement; (vi) the language in which the witness is most comfortable (where a hearing interpreter is required).
Drafting standards and best practices
First-person narrative: Witness statements should read in the witness's own voice — first person, plain language, avoiding legal argument. If the statement reads like a legal brief, it loses credibility. Tribunals are experienced in identifying over-lawyered statements; they discount them.
Fact not argument: The witness speaks to what they personally observed, communicated, or decided. They should not characterise the counterparty's conduct as a breach or assess whether a contract was valid. Legal argument belongs in the memorial; factual narrative belongs in the witness statement.
Contemporaneous documents: Anchor every key factual point in a contemporaneous document (email, meeting minute, contract approval, payment record). Unsupported recollections of events from 3–5 years ago are inherently less reliable than recollections confirmed by contemporaneous documents. For every significant factual point in the statement, ask: "What document backs this up?"
Deal with adverse facts: A witness who ignores adverse facts and documents is more vulnerable in cross-examination than one who addresses them directly and provides context. Brief your witness: anticipate the most damaging cross-examination questions and address them in the witness statement, either by providing context, alternative explanation, or conceding irrelevant points.
Preparing witnesses for cross-examination
Cross-examination preparation is as important as statement drafting. Steps: (i) Review all documents the witness is mentioned in — the counterparty's counsel will have reviewed the same documents; (ii) identify the 3–5 most damaging documents or contradictions and develop the witness's response to each; (iii) conduct a mock cross-examination session focusing on the difficult documents — witnesses are rarely experienced with hostile questioning and need practice; (iv) advise the witness: answer only the question asked; do not volunteer additional information; pause before answering; say "I don't know" or "I don't recall" rather than guessing; (v) remind the witness that their duty is to the tribunal, not to the party — a witness who appears to advocate rather than testify loses credibility rapidly.
Practical checklist
- Statement exchange schedule: agree witness statement exchange date at first CMC — simultaneous exchange is standard; sequential exchange is sometimes agreed for complex cases
- Witness identity: identify witnesses early — employees may leave the company; key decision-makers may be unavailable
- Language: confirm whether witnesses require interpreters at the hearing — notify the tribunal in advance; check institutional rules on interpretation costs
- Contemporaneous docs: compile the witness's relevant documents before drafting the statement — drafting around documents produces better statements
- Cross-examination prep: schedule at least 2 preparation sessions per witness — one document review, one mock cross-examination
- Hot-tubbing: for expert witnesses, propose concurrent expert examination (hot-tubbing) at first CMC — saves 2–4 hearing days in complex cases
What we'd typically advise
The most common witness statement error we see is over-drafting — a 100-page witness statement covering every document in the case, written by counsel rather than the witness. These statements are ineffective. A 20-page, clearly written statement covering 10 core factual points, each anchored in contemporaneous documents, is more persuasive than a 100-page treatise. The tribunal needs to trust the witness — and trust comes from credibility, which comes from clarity and honesty, not comprehensiveness.
Frequently asked questions
Can a witness submit a supplemental witness statement after the initial exchange?
Only with tribunal permission. Most procedural timetables permit one round of witness statements. Supplemental statements responding to the counterparty's statements may be permitted on specific issues — request permission from the tribunal at the case management conference and explain why a supplemental statement is necessary.
What if a key witness refuses to testify or is unavailable?
A party cannot compel a witness to testify in arbitration (unlike court proceedings where subpoenas are available). If a key witness is unavailable, consider: admitting a written record of their observations without cross-examination (subject to the weight the tribunal gives it); using documents in lieu of oral testimony; seeking a procedural order from the tribunal requesting the counterparty to make specific individuals available for questioning.
Are witness statements filed with the arbitral institution?
Generally no — witness statements are exchanged between the parties and submitted to the tribunal, not filed with the institution. The institution does not review the substance of witness statements. Confidentiality of witness statements is governed by the arbitration's confidentiality provisions.
Can a party submit a witness statement from a former employee?
Yes. Former employees can provide witness statements, though cooperation may be more difficult to obtain. Former employees are not bound by any professional obligation to cooperate. Consider obtaining a written undertaking from the former employee at the time of departure regarding cooperation in future proceedings if they were involved in a significant transaction.
What is hot-tubbing and when is it appropriate?
Hot-tubbing (concurrent expert evidence) is a procedure where multiple party-appointed experts on the same issue are examined simultaneously by the tribunal, answering the same questions and responding to each other. It is most effective for expert evidence on discrete, well-defined technical issues (e.g., quantum methodology, delay analysis methodology). It can save 2–4 hearing days in complex cases. Propose it at the first CMC for disputes involving competing expert reports on quantified issues.
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Published 20 May 2026. General information only — not legal advice. Contact us for matter-specific advice.