This study examines the combined impact of fintech and financial inclusion on achieving the United Nations’ Sustainable Development Goals (SDGs). Previous research has emphasized the role of financial inclusion in reducing poverty, strengthening resilience, and promoting economic stability; however, its interaction with fintech in advancing sustainability remains less examined. Using four composite indices incorporating updated variables, expanded country coverage, and a broader temporal scope, this analysis evaluates digital financial channels, including formal access, mobile money, digital credit, transfers, and rural finance, across SDGs 3, 4, 8, and 9. The findings indicate that formal access is associated with lower maternal mortality (SDG 3) and contributes positively to decent work and economic growth (SDG 8), as well as industry, innovation, and infrastructure (SDG 9). Digital credit and transfers help ease liquidity constraints in high-inequality regions, while mobile money enhances education outcomes (SDG 4) under robust governance, supporting informal labor markets. Rural finance strengthens innovation and infrastructure development in underserved areas, reinforcing SDG 9. A simultaneous equation model provides evidence of bidirectional relationships among financial inclusion, fintech adoption, and sustainable development, underscoring their mutual reinforcement rather than strict causality. Overall, the study highlights the systemic interconnection between finance and sustainability and emphasizes the importance of governance, infrastructure, and regulation in maximizing developmental benefits.