The soft power of higher education, grounded in institutional attractiveness, scholarly authority, and the capacity to shape international preferences, plays a pivotal role in the evolving architecture of science diplomacy and foreign policy. This study aims to provide a systematic explanation of how this can be operationalized in response to transnational challenges, addressing the theoretical gap between higher education and science diplomacy. The framework synthesizes five core components: Nye's soft power, AAAS's tripartite model (2010), Gluckman et al.'s interest-driven approach (2017), Flink and Schreiterer's strategic trinity (2010), and McClory and Raimzhanova's independent role of higher education in soft power. Using a qualitative design with directed content analysis of 92 library-based sources published between 1990 and 2025, findings reveal that: (1) soft power of higher education manifests most in the "Science for Diplomacy" dimension; (2) the three strategic goals of Access, Advancement, and Influence form a cumulative logical hierarchy that paves the operational pathway for this power; (3) countries under sanctions can leverage the scholarly authority of specialized institutions (exemplified by Iran's Royan Institute) to mitigate political constraints; and (4) science diplomacy simultaneously serves as a sphere for cooperation, competition, and influence. The primary innovation lies in proposing a six-layer conceptual model with a positive feedback loop, explicating the precise mechanism through which academic capacities are converted into soft power and strategically directed within science diplomacy. This study implies that scientific expertise and institutional credibility can substantially moderate political limitations, transforming science diplomacy into an effective channel for managing transnational challenges.