Sustainable management of human activities affecting Atlantic marine ecosystems is critical to maintain its health and to support the blue economy of the bordering countries. TRIATLAS will contribute to this by delivering knowledge of the current state and future changes of the Atlantic marine ecosystems. We achieve this through a basin-wide approach integrating research from the North and South, that closes critical knowledge gaps in the Tropical and South Atlantic which impede an understanding of the entire basin. We bring together an interdisciplinary team of marine ecologists, physical oceanographers, climate researchers, and social scientists from 34 different institutions in Europe, Africa, and South America, together with multisectoral and regional stakeholders. We will enhance knowledge of the marine ecosystems in key areas of the Atlantic using existing and pivotal new (physical, biological, societal) observations. Earth system, ecological, and socio-economic models and observations will be used to assess the cumulative impacts of (climatic, pollution, and fishing) pressures driving fluctuations in the marine ecosystem, and the potential for tipping point behavior and regime shifts. We will develop the first predictions of the marine-ecosystem for the next 40 years for the whole Atlantic, by combining state-of-the-art climate prediction and ecosystem models, with Shared Socioeconomic Pathways, and by conducting socio-economic vulnerability assessments services, with stakeholder engagement. TRIATLAS will enhance capacity in marine ecosystems, oceanography, and climate research in countries bordering the South and Tropical Atlantic Ocean. There will be close cooperation and alignment with relevant European Commission services and the South-South Framework for Scientific and Technical Cooperation, as well as other relevant initiatives in the field. We will contribute to upscale cooperation around the Atlantic.