Unilateral arbitrator appointment fails without express written waiver; participation alone does not cure statutory ineligibility.

A sole arbitrator unilaterally appointed by one party is treated as ineligible where the statutory bar on appointment applies, and that ineligibility can be displaced only by an express post-dispute agreement in writing. Mere participation in the proceedings, a no-objection confirmation, or requests for extension of time do not satisfy the waiver requirement. If no valid written waiver exists, the appointment remains invalid and the arbitrator's mandate terminates in law, requiring substitution.

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Issues: Whether the sole arbitrator appointed unilaterally by one party was rendered ineligible under Section 12(5) of the Arbitration and Conciliation Act, 1996, and whether subsequent participation or requests for extension constituted an express waiver in writing.

Analysis: The governing principle is that ineligibility under Section 12(5) is displaced only by an express agreement in writing made after disputes have arisen. Mere participation in the arbitral proceedings, confirmation of no objection, or requests seeking extension of time do not satisfy that statutory requirement. Once a person falling within the statutory bar is appointed, the appointment is invalid in law and the mandate terminates under Section 14(1)(a) unless there is a valid written waiver.

Conclusion: The unilateral appointment could not be sustained, no express waiver in writing was shown, and the learned sole arbitrator's mandate stood terminated. The petition was allowed and a substitute arbitrator was appointed.

Ratio Decidendi: A statutory disqualification under Section 12(5) of the Arbitration and Conciliation Act, 1996 can be waived only by an express post-dispute agreement in writing, and conduct or procedural participation cannot amount to such waiver.

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