ABSTRACT Motivated by the global sustainability imperative, this paper reveals that ESG committees boost corporate sustainable performance in Chinese A + H firms by balancing conforming legitimacy (norm adherence) and strategic legitimacy (stakeholder engagement). Ownership structure moderates outcomes, and effectiveness rises in firms prioritizing core stakeholders or having gender‐diverse boards but diminishes with strong internal controls. The findings advance legitimacy theory by integrating institutional and strategic perspectives. Practical guidance urges firms to establish ESG committees, tailor strategies to ownership contexts, and leverage board diversity. Policymakers should refine guidelines for emerging markets balancing state and market forces.