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This work provides an integrated experimental and computational assessment of the cationic surfactant Quaternium-22 (Q-22) as a potentially eco-compatible corrosion inhibitor for carbon steel (CS) in 1 M hydrochloric acid. Gravimetric analysis and electrochemical techniques: electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) were employed over a 20–50 °C temperature range. Q-22 exhibited mixed-type inhibition behavior, with efficiency rising to 97% at an optimal concentration of 277 μmol L⁻¹. Performance was concentration-dependent but diminished with increasing temperature, indicating partial inhibitor desorption at elevated temperatures. Thermodynamic evaluation confirmed a spontaneous adsorption process aligned with the Langmuir isotherm, involving a mixed physisorption and chemisorption mechanism. Surface characterization via scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle (CA) measurement, and X-ray photoelectron spectroscopy (XPS) verified the formation of a coherent, hydrophobic inhibitor layer that substantially reduced surface roughness and corrosion damage. Theoretical validation using density functional theory (DFT), natural bond orbital (NBO) analysis, and molecular dynamics (MD) simulations revealed strong adsorption energetics and favorable electronic properties consistent with the inhibitor’s high experimental efficacy. The collective findings establish Q-22 as a potent, eco-compatible corrosion inhibitor for CS in acidic environments, operating through a robust adsorptive film-forming mechanism.