Marine spatial planning (MSP) has emerged as a critical legal and policy instrument for harmonizing economic development with environmental sustainability in maritime governance. As a nation with an extensive and resource-abundant maritime domain, Vietnam faces challenges in spatial resource management, including jurisdictional fragmentation, inter-sectoral conflicts, climate change-induced vulnerabilities, and regulatory ambiguities in offshore economic activities. The adoption of Decree 139/2024/QH15 in mid-2024 marks a significant milestone in Vietnam’s commitment to MSP, aiming to resolve transboundary maritime conflicts, optimize marine zoning for economic development, and reinforce the country’s blue economy strategy. However, persistent legal and institutional deficiencies continue to hinder the effective operationalization of MSP, particularly in relation to spatial zoning, interagency coordination, and offshore wind energy regulation—critical to Vietnam’s Net Zero emissions target by 2050. This study employs a comparative legal analysis alongside case studies, to assess the implementation of MSP at both national and local levels. By examining regulatory frameworks governing MSP in jurisdictions with established best practices—including the European Union, Australia, China, and the United States—this research identifies structural deficiencies in Vietnam’s MSP system and proposes targeted reforms. The findings underscore the urgency of a cohesive legislative framework, enhanced regulatory integration, and an ecosystem-based governance model to align with international best practices. While primarily focused on Vietnam’s legal and policy context, this study also contributes to broader discourses on sustainable ocean governance, legal harmonization in MSP frameworks, and environmental regulatory integration.