The corrosion inhibition performance of Cynodon dactylon aqueous extract (CDAE) toward copper in 3.5 wt.% NaCl solution was comprehensively investigated using electrochemical, surface, and thermodynamic approaches. The phytochemical composition of the extract was initially characterized by GC-MS analysis, revealing the presence of oxygen- and nitrogen-containing organic compounds capable of interacting with the copper surface. The anticorrosion behavior of CDAE was evaluated through potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements at different inhibitor concentrations and temperatures. Electrochemical results demonstrated that CDAE acts as an effective mixed-type inhibitor, significantly reducing the corrosion current density and increasing the charge transfer resistance. The inhibition efficiency increased with inhibitor concentration and reached a maximum value of 91.63% at 300 mg L-1 according to EIS analysis. The decrease in double-layer capacitance confirmed the adsorption of inhibitor molecules and the engineering of a compact nanoporous bio-derived interfacial protective layer on the copper surface. SEM-EDS analyses further verified the substantial reduction in surface deterioration in the presence of CDAE. Temperature-dependent studies indicated that the inhibition efficiency decreases with increasing temperature, suggesting a predominantly physical adsorption mechanism. Thermodynamic parameters, including activation energy, enthalpy, and entropy, supported the spontaneous adsorption behavior and interfacial stabilization process of the inhibitor film. Overall, the findings demonstrate that CDAE is a highly efficient, eco-friendly, low-cost, and sustainable green inhibitor capable of promoting stable nanoporous protective interfacial layer formation for corrosion mitigation of copper in chloride-containing environments.