Evidence informed decision making has emerged as one of the most critical pillars of modern health service management and public health governance. In an era characterized by rapidly evolving healthcare technologies, expanding clinical knowledge, and complex organizational challenges, health systems can no longer rely on intuition, tradition, or political expediency alone. Instead, there is a growing global movement toward integrating the best available research evidence, professional expertise, stakeholder values, and contextual realities into managerial and policy decisions. Despite this theoretical consensus, the practical application of evidence informed decision making remains inconsistent and often weakly institutionalized. Hospital executives, middle and senior managers, and public health leaders frequently face structural, cultural, cognitive, and political barriers that prevent systematic use of evidence in everyday decisions. This article develops a comprehensive, competency driven framework for understanding how evidence informed decision making can be strengthened in health service management and public health systems. Drawing exclusively on the scholarly and institutional references provided, the study synthesizes research on managerial competence, evidence based and evidence informed management, organizational learning, policy translation, and health system governance. It advances the argument that evidence informed decision making is not merely a technical skill but a deeply embedded professional competence that depends on leadership, organizational culture, access to knowledge, and the ability to integrate multiple forms of evidence. The article also addresses the persistent divide between academic research and managerial practice, demonstrating how this gap undermines both the relevance of research and the quality of decision making. Through extensive theoretical elaboration, the study shows how frameworks such as the GRADE Evidence to Decision approach, knowledge translation platforms, and competency based leadership models can be integrated into a coherent system that supports evidence use across all levels of healthcare organizations. The results of this conceptual analysis indicate that improving evidence informed decision making requires long term investment in managerial education, continuous professional development, institutional incentives, and supportive policy environments. The discussion further explores the ethical and practical implications of evidence use, including issues of power, transparency, and contextual adaptation. By situating evidence informed decision making within the broader ecosystem of health governance, this article contributes to a deeper understanding of how competent managers and policymakers can drive sustainable improvements in health system performance, equity, and population health outcomes.