Circumventing inherent embrittlement, poor heat resistance, and melt elasticity of poly(lactic acid) (PLA) without compromising its remarkable stiffness and strength has become a particular challenge in polymer science due to increasing demand for green materials in emerging applications of sustainable chemistry and engineering. Achieving this without using any high-cost reagent/additive and/or complex processing technique is another critical aspect for developing industrially viable alternatives to petroleum-based commodity plastics. Here we demonstrate that high-shear mixing of PLA with waste cross-linked polyurethanes and waste cellulose fibers allows for overcoming its inherent embrittlement, poor heat resistance, and melt elasticity without compromising its superior stiffness and strength while suggesting a sustainable way of recycling/reusing industrial wastes as high added-value additives. We therefore achieve to produce stiff, strong, super-tough, and heat-resistant PLA-based green materials, for instance, with an elastic modulus of 4 GPa at 25 °C (~30% higher than that of pure PLA), a storage modulus of 312 MPa at 90 °C (~44 times higher than that of pure PLA), a tensile strength of 65 MPa (comparable to that of PLA), and an impact strength (toughness) of 52 kJ/m2 (~2.3 times higher than that of pure PLA).