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Arbitrator Disclosure in 2026: Three Rules That Still Catch Arbitrators Off Guard
Awards worth hundreds of millions of euros have been annulled in recent years. Not because the underlying arbitration was procedurally flawed. Not because the tribunal got the law wrong. Because an arbitrator failed to disclose something a party was entitled to know.
The duty to disclose is not controversial. Every major set of institutional rules acknowledges it. The IBA Guidelines codify it. Arbitrators understand it exists. And yet disclosure failures remain among the most common — and most costly — causes of challenge proceedings and set-asides.
The problem is not ignorance of the rule. It is a persistent misjudgement of its scope. Here is where that misjudgement most often occurs — and what to do about it.
- Repeat appointments: the pattern matters, not the individual appointment
A single prior appointment by the same counsel or party rarely raises a concern. Taken in isolation, it tells you little. But a pattern of appointments — even individually unremarkable ones — can be a different matter entirely.
This is particularly acute in specialised practice areas, where the pool of available arbitrators is limited and repeat interactions are structurally inevitable. The question is not whether any single appointment crosses a threshold. The question is whether a reasonable third party, fully informed of the entire pattern, would have justifiable doubts about independence.
What to do: Before accepting any appointment, map the full history of prior engagements with appointing parties and their counsel — not just the most recent one. If the cumulative picture could raise questions, disclose it. Do not wait for the other side to find it.
- Personal history: the relationship you have decided is irrelevant is exactly the one to disclose
The obligation to disclose is not limited to professional relationships. Prior friendships, social connections, and past disputes fall within its scope. The age of the relationship — or the arbitrator's own assessment of its irrelevance — does not extinguish the duty.
The governing principle is straightforward, even when its application is uncomfortable: the decision about materiality belongs to the parties, not the arbitrator. Disclosure transfers that decision to where it belongs. Non-disclosure does not.
Recent annulment proceedings have made this concrete. High-value awards have been set aside on the basis of personal connections that the arbitrator considered immaterial and therefore withheld. The institution or court reviewing the challenge reached a different view — and the award did not survive.
What to do: Apply the objective test, not the subjective one. The question is not whether you consider a prior relationship relevant. The question is whether a reasonable party, aware of it, might. If the answer is arguably yes, disclose.
- Social media and public statements: your LinkedIn post may be your next challenge ground
This is the area where disclosure practice is developing fastest — and where arbitrators are most exposed.
Arbitrators increasingly maintain public professional profiles. They publish commentary on LinkedIn, contribute to academic debate, participate in policy initiatives, and speak at conferences. These are legitimate and valuable activities. They are also, in certain disputes, potential grounds for a challenge based on apparent prejudgement.
The test is not whether the statement was made in a professional rather than personal capacity. The test is whether a reasonable observer could read it as bearing on the matter in dispute. Proximity to the issues at stake, timing relative to appointment, and specificity of the statement all factor into the analysis — but none of them substitutes for the objective observer test.
What to do: Before accepting an appointment, review your recent public statements on issues proximate to the dispute. If any statement could reasonably be read as bearing on the case, disclose it at the outset — before the question is raised by the other side.
The IBA Guidelines are a starting point, not a safe harbour
The IBA Guidelines on Conflicts of Interest in International Arbitration remain the most widely used framework for navigating these questions. Their traffic-light system — Red, Orange, and Green Lists — offers a degree of predictability that parties and institutions rely on.
But the Guidelines are not exhaustive, and they carry no binding force of their own. Circumstances not appearing on any list may still require disclosure if they would cause a reasonable third party to have justifiable doubts. The Guidelines say so themselves.
Some of the failures that have led to annulment involved circumstances that fell between the lists — situations requiring independent judgment rather than a lookup table. An arbitrator who treats compliance with the Orange List as the end of the analysis, rather than its starting point, misunderstands the nature of the instrument.
The limit of "when in doubt, disclose"
A near-orthodoxy has taken hold in arbitration practice: when in doubt, disclose. The logic is sound. Disclosure shifts the risk of challenge to the parties; proceeding without objection protects the arbitrator. Non-disclosure creates an information asymmetry that institutions and courts have shown little patience for.
But the orthodoxy requires qualification. Over-disclosure carries its own costs. An arbitrator who discloses every tangential connection risks signalling a lack of judgment about what actually matters. The goal is not maximum disclosure. It is accurate identification of what a reasonable party would want to know. These are not the same thing.
Three practical rules
Apply the objective test early — and revisit it. The question is whether a reasonable observer, fully informed, would have justifiable doubts. Apply it rigorously at the time of appointment. Apply it again whenever new information emerges during the proceedings. The duty is continuous.
Treat your public profile as part of your pre-appointment review. Before accepting an appointment, check your recent positions on issues close to the dispute. Identify what a reasonable party might consider meaningful. Disclose it before someone else raises it.
Document the reasoning when you decide not to disclose. If you conclude that a circumstance does not require disclosure, record that analysis. If the issue is later raised in annulment proceedings or before an appointing authority, the ability to show that it was identified, considered, and assessed against the applicable standard will materially change your position.
The cases that have gone wrong share a common feature: the arbitrator assessed the relevant circumstance through their own frame of reference and concluded it did not matter. The state court, the annulment committee, or the appointing authority reached a different view.
That gap — between how arbitrators see themselves and how they are seen — is where disclosure failures originate. In a field built on the trust of parties who have chosen to opt out of state court litigation, the perspective of the reasonable outside observer is not optional. It is the job.
The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.
