Mapping organic carbon (OC) stores in marine sediments is a management priority to potentially minimize the anthropogenic release of organic carbon from the seabed. Sediment OC content shows high regional variability, shaped by a complex interplay of physical, chemical, biological and anthropogenic factors. In this study, we present an assessment of the drivers and patterns of sediment OC across European regional seas, with a particular focus on the role of large-scale habitats, substratum characteristics, and environmental conditions. To investigate these relationships, we integrated data sets encompassing sediment OC, benthic habitats, sediment substrata and 11 environmental variables. Applying machine learning techniques, we identified wave exposure (estimated from wave fetch), light availability, seafloor geomorphic features, and maximum bottom water temperature as the most important environmental predictors of sediment OC content across European regional seas. While the model captured broad spatial patterns in sediment OC, it did not resolve local scale variability, making it better suited for regional assessments than for site-specific predictions. Overall, the highest OC contents were found in sediments underlying vegetated habitats such as Posidonia oceanica and other seagrass meadows as well as in mud, and mixed sediment substrata. OC hotspots were generally located in inshore areas with low wave fetch and temperature; these include areas of the Baltic Sea, North Sea, Adriatic Sea, Barents Sea, and the Black Sea. Our data-driven approach provides a robust foundation for identifying OC-rich sediments, which are critical for conservation planning and assessing anthropogenic impacts on marine OC.