Marine protected areas (MPAs) have proliferated to protect marine ecosystems and manage unsustainable fishing, but their outcomes vary by economic and governance contexts. Drawing on a panel dataset spanning 1995–2021 and employing the Pressure–State–Response framework, this study analyses how MPA coverage is associated with overexploited fish stocks and examines Official Development Assistance (ODA). Results show MPAs in high-income countries are associated with lower overexploited catch rates, reflecting robust governance. In low-income nations, however, limited capacity is often linked to ‘paper parks’ with negligible impact. Multi-purpose ODA – supporting sustainability goals – appears more effective than single-purpose ODA and is associated with better conservation outcomes. Integrating MPAs with fisheries management, supported by international assistance for enforcement, appears important for bridging disparities in effectiveness. By highlighting the interplay among economic conditions, governance and funding, this study offers higher-level insights into factors that shape MPA effectiveness, contributing to broader policy discussions on marine conservation.