<p>Mangroves and seagrasses are vital coastal ecosystems that boost biodiversity, regulate environmental processes, and support human well-being. Individually, these habitats serve as nursery grounds, facilitate nutrient flux, provide coastal protection, mitigate climate change through carbon sequestration, and support local livelihoods. However, a thorough review of their combined contributions is limited. This study presents a systematic review of publications on the synergistic benefits arising from the connectivity between mangroves and seagrasses. Using the Millennium Ecosystem Assessment framework to examinemangrove–seagrass connectivity and identify research trends, gaps, uncertainties, and future directions. The synthesis indicates that these ecosystem services primarily focus on supporting services, particularly habitat provision for mobile fauna. Mangrove–seagrass connectivity also maintains biomass productivity, nutrient cycling, carbon stocks, and coastal protection, while provisioning and cultural services have limited socio-economic impact. Many potential services remain underrepresented and lack interdisciplinary research. Moreover, mangrove–seagrass connectivity acts as a fundamental ecosystem in seascape ecology, supporting early-stage development of coral fish, nutrient reservoirs, and long-term blue carbon sequestration. Of the 17 Sustainable Development Goals (SDGs), goals 14, 15, 13, 12, and 6 are most relevant to these ecosystems. Therefore, expanded ecosystem assessments and interdisciplinary approaches are recommended to enhance research, conservation, and sustainable management.</p>