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September 23, 2026

Non-signatories and Arbitration Agreements under Thai Law

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The Legal Industry Reviews

Arbitration under Thai law rests on consent. Section 11 of the Arbitration Act B.E. 2545 (2002) requires an arbitration agreement to be in writing and signed by the parties. This may also be satisfied by communications, an unchallenged allegation in pleadings, or incorporation by reference to a document containing an arbitration clause. A non-signatory cannot, as a general rule, be compelled to arbitrate merely because it participated in the transaction, received a benefit, or belongs to the corporate group of a signatory. Thai law nevertheless permits arbitration agreements and awards to affect third parties indirectly in limited circumstances.

Under section 24, an arbitration clause is separable from the main contract; the invalidity of the contract does not invalidate the clause. In Supreme Court Judgment No. 3918/2563, an apparent sales contract concealed a construction contract and was void under the Civil and Commercial Code. However, the concealed construction contract and written arbitration clause remained effective. The tribunal had jurisdiction, and its award was enforceable under the Arbitration Act.

Under the Arbitration Act, when a claim or liability is validly transferred, the transferee is bound by the related arbitration agreement. This includes assignment, transfer of obligations, legal succession, and subrogation. Depending on the facts and contract and agency law, consent may arise through execution by an authorized agent, ratification, assumption of obligations, or conduct accepting the contract and its arbitration clause. Thai law respects separate corporate personality. The group-of-companies doctrine has no statutory basis under the Arbitration Act, while alter egos or sham allegations require compelling evidence and an identifiable legal basis.

Supreme Court Judgment No. 9161/2568 illustrates the procedural treatment of non-signatories. A consultancy contract required LCIA arbitration seated in Dubai. When the employer sued a consultant and his spouse in Thailand concerning a housing loan, the court disposed of the claim against the consultant because he invoked the arbitration agreement. His spouse was not a party to that agreement and could not be referred to arbitration. However, because the debt was a joint marital debt, the court stayed the claim against her pending the award, which would affect her liability. Thai courts neither compel non-signatories to arbitrate nor permit related litigation to undermine arbitration.

An award may affect third parties indirectly through accessory obligations. In Supreme Court Judgment No. 7125/2568, a tribunal had held that a construction contract was voidable for mistake as to personal qualifications and became void upon avoidance, requiring restitution under Civil and Commercial Code section 176. The employer sued the bank issuing a performance guarantee. The Supreme Court held the employer bound by the award’s determination that the principal contract was void. Because suretyship under section 681 secures only a valid obligation, the guarantor was discharged. The award did not bind the bank as a party; its determination of the principal obligation affected the accessory guarantee.

Practitioners should distinguish jurisdiction over a non-signatory from procedural coordination and an award’s indirect consequences. Where a sustainable legal basis exists, the non-signatory should be joined during the arbitration, and the award should record the jurisdictional basis and determine liability. Naming a third party without consent or another recognized basis is insufficient, while imposing liability only at the enforcement stage remains more difficult and challenging.

 

This article was first published in the September 2026 Thailand edition of The Legal Industry Reviews, an international platform that publishes news and applied law updates from industry-leading law firms worldwide. To browse the latest complete issue, please visit The Legal Industry Reviews website.

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