Dual-purpose financial systems that integrate Islamic and conventional finance offer an untapped potential for inclusive and sustainable growth. While conventional banking often holds the majority of assets and plays a significant role, the distinct features of Islamic finance, such as its emphasis on risk-sharing and financial inclusion, can complement the shortcomings of the conventional system. However, the realization of this potential hinges on coherent governance arrangements, legal harmonization, and institutional capacity, which are often underdeveloped even in pioneer nations. This paper proposes a conceptual framework to assess the dual systems and investigates whether they can contribute to development and inclusive growth. Through a comparative case study analysis of Malaysia, a state-led model with strong institutional frameworks, and Indonesia, a more gradual, market-driven approach facing ongoing challenges, we identify the governance conditions that are prerequisites for success. The paper concludes that a successful dual-purpose system requires deliberate cultivation of a stable legal and regulatory environment to ensure philosophical alignment and economic performance.