This study integrates Sustainable Energy Development (SED) with an Energy Ecosystems (EE) framework in Greece to reveal how macrolevel policies, mesolevel infrastructures, and microlevel behaviors shape energy transitions. Drawing on historical data primarily spanning 2010–2024, supplemented by 16 semi-structured expert interviews and a macro–meso–micro analytical approach, it examines SED dimensions—affordability, supply, consumption, and security—within the supplier–producer–distributor–consumer nexus. The findings show notable progress in solar and wind adoption but also underscore persistent challenges such as high import dependency, regulatory inefficiencies, and infrastructural gaps. By proposing targeted policy directions and suggesting a new modus operandi of local-level institutional coordination, the research illustrates how an SED–EE synergy can foster resilience, innovation, and social equity, thereby informing sustainable energy strategies not just for Greece but also for other regions facing similar structural hurdles. The novel integrative perspective of this paper, unlike prior approaches that address either macropolicy targets or microlevel entrepreneurial activity alone, clarifies how mesolevel dynamics facilitate or hamper SED goals. This theoretical and practical synthesis is expected to inform the design of more resilient, equitable, and innovation-driven energy policies.