The corrosion inhibition behavior of a naphthoxazinone derivative 1-phenyl-1,2-dihydronaphtho[1,2-e][1,3]oxazin-3-one (PNO) on J55 steel in 3.5 wt% NaCl solution saturated with carbon dioxide was evaluated using weight loss, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The surface morphology on the metal sample was analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The adsorption of PNO obeyed the Langmuir isotherm. The results of potentiodynamic polarization indicated that the PNO molecule behaved as a mixed type inhibitor by reducing both the anodic and the cathodic electrochemical reactions. The surface analysis showed that the metal surface is considerably smoother and with more uniform morphology in the presence of the inhibitor. DFT based quantum chemical calculations and molecular dynamic (MD) simulations supported the experimentally obtained results.