The implementation of the blue economy has emerged as a strategic approach to achieving sustainable development in island tourism destinations by balancing environmental conservation, economic growth, and social well-being. Despite its growing significance in both policy and academic discussions, empirical evidence identifying the key determinants of successful blue economy implementation in island tourism remains limited. This study seeks to identify and validate the critical factors influencing the successful development of the blue economy in the island tourism sector of the Seribu Islands Regency, Indonesia, using the Delphi method. A descriptive–qualitative research design was employed through a two-round Delphi process involving 27 expert respondents representing academia, government institutions, tourism practitioners, environmental organizations, financial institutions, and local communities. An initial set of twenty variables, derived from a comprehensive review of the relevant literature, was evaluated to determine their relevance and level of consensus. The results revealed that seventeen variables satisfied the predefined consensus criteria and were considered significant, whereas three variables did not achieve sufficient agreement among the experts. The five highest-ranked variables were local economic benefits, government policy and regulatory support, stakeholder collaboration, marine ecosystem conservation, and sustainable tourism infrastructure. These findings highlight that the successful implementation of the blue economy in island tourism depends on an integrated governance framework that simultaneously strengthens environmental sustainability, economic resilience, social participation, institutional capacity, technological innovation, and financial support. The validated variables provide a robust empirical foundation for policymakers, tourism destination managers, and researchers in designing evidence-based strategies and policies that promote sustainable island tourism development and advance the implementation of blue economy principles in Indonesia.