Date seeds were subjected to electrochemical analysis to inhibit the corrosion of mild steel in an acidic medium of 1 M HCl. The inhibitor inhibition efficacy was studied by gravimetric spectroscopy, potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS). The results revealed that oil extracts from date pits functioned as cathodic rather than anodic inhibitors, and the maximum corrosion inhibition efficiencies were obtained with an optimal concentration of 700 ppm—adsorption of these extracts on the mild steel surface followed by the Langmuir isotherm. The SEM and EDX characterization confirms the existence of a protective layer on the metal surface. Quantum chemical calculations using the density functional theory (DFT) method was also performed to understand the inhibition and adsorption behavior of the main constituents of Date Seed extract on the Fe surface.