The swift growth of the automobile industry has resulted in the generation of huge quantities of waste rubber from end‐of‐life tires. Incidentally, the humungous quantities of waste plastics that are an integral part of the legacy landfills/dumpsites, lying unattended and about which not many valorization schemes are available, pose various geoenvironmental issues apart from occupying a lot of landfill space. These situations might end up being a blessing in disguise if a strategy to utilize both waste rubber and waste plastic, segregated post landfill/dumpsite biomining, in tandem by manufacturing polymer composites by resorting to extrusion process followed by the injection molding, for different engineering applications. Thus, the physical, mechanical, thermal, morphological, and leaching properties of the manufactured polymer composites were evaluated in this study. The tensile strength and impact resistance of polymer composites were between 4.3–26.9 MPa and 9.4–20 kJ/m2, respectively. Their glass transition temperature lies between −81.13 and − 50.04°C. The leachable concentration of heavy metals and organic compounds was within acceptable limits for drinking water and permissible limits for inland surface water disposal. Therefore, this study contributes valuable insights into using waste materials for polymer composites manufacturing, which would be further helpful in achieving sustainable development goals and circular economy.