In this study, systematic investigations were conducted to solidify dredged marine sediments using the low-carbon composite binder made by mixing Ordinary Portland and calcium sulfoaluminate cement (OPC-CSA). A series of tests to evaluate physical and mechanical properties of samples, which indicated that the OPC-CSA composite binder could effectively improve the engineering characteristics of solidified dredged marine sediments, such as the immediate California Bearing Ratio (I-CBR) index, unconfined compressive strength, splitting tensile strength, and elastic modulus. In addition, simple models were proposed to correlate the unconfined compressive and splitting tensile strength with the elastic modulus of treated sediments. Importantly, the elastic modulus of treated sediments was defined by the local small-strain sensor method. In addition, the correlation between the strength and the three kinds of failure mode of the specimens was revealed. Lastly, simplified carbon footprint analysis indicated that OPC-CSA composite binder offers potential CO2 emissions savings of 14%-41%. The laboratory tests have revealed that the mechanical and environmental behaviors of solidified dredged marine sediments meet the environmental and engineering requirements of the standards and regulations. Low-carbon and sustainable OPC-CSA composite binder-solidified dredged marine sediments could be reused as subbase or roadbed infill materials for low traffic.