Organizations’ rapid adoption of third-party AI platforms has created governance challenges that existing frameworks do not yet adequately address. Unlike traditional IT vendors, AI platforms combine algorithmic opacity, rapid technological change, and concentrated market power, creating novel dependencies that violate a core assumption of established governance frameworks: that organizations control their technology infrastructure. To address this gap, this paper conceptualizes the Platform Liaison Role—a dedicated governance mechanism that bridges organizational AI strategy with third-party platform operations. Drawing on IT Governance Theory, Resource Dependence Theory, and Agency Theory, we specify three core mechanisms (communication routines, policy translation, and joint risk management), antecedents, boundary conditions, and mediation pathways for this role. Through theoretical derivation, we present five testable research propositions and implementation guidance. This paper extends governance frameworks to address external AI platform dependencies and provides practitioners with actionable guidance for establishing effective AI platform governance.