<p>The study focuses on developing eco-friendly composites using eggshell and marble powder, with varying weight percentages from 0 to 60% (by wt). The composites are produced by open-cast molding, and mechanical characterization examines the effects of these materials. Results indicated that decreasing eggshell content increases composite density, with pure marble powder composites being 11% denser than those reinforced solely with eggshell. Hardness increases with marble powder, with a 60% (by wt) marble composite exhibiting a 17.21% improvement in hardness over a 60% (by wt) eggshell composite. However, the tensile strength of a 60% (by wt) eggshell composite is 43.56% higher than that of a 60% (by wt) marble composite. A hybrid composite with 50% (by wt) eggshell and 10% (by wt) marble demonstrates 10.67% greater flexural strength and 10.9% higher impact strength than a 60% (by wt) eggshell composite. Additionally, a hybrid with 10% (by wt) eggshell and 50% (by wt) marble exhibits a 52.45% increase in impact strength compared to the reverse composition. Fractography reveals that eggshell particles contribute to crack initiation and propagation, while marble powder enhances overall fracture toughness. The MADAM-TOPSIS approach identifies the marble powder-only composite as the best performer in overall physio-mechanical properties, while hybridization with eggshell and marble powder results in balanced mechanical properties.</p> Graphical abstract <p></p>