The iminium surfactant p-benzylidene benzyldodecyl iminium chloride was synthesized, characterized and evaluated as a novel corrosion inhibitor for plain carbon steel in 1 M HCl solution at 30, 40, 50 and 60 °C using gravimetric analysis, spectrophotometric analysis of iron ions, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and density functional theory (DFT). The evaluated compound acted as an efficient corrosion inhibitor for plain carbon steel in 1 M HCl solution. The inhibition efficiency of the compound increased with an increase in concentration and solution temperature. The iminium surfactant gets adsorbed onto the plain carbon steel surface via mixed types of adsorption with predominantly chemisorption. The adsorption of the inhibitor was found to follow the Langmuir adsorption isotherm. The surface morphology of corroded plain carbon steel in uninhibited and inhibited acid, as investigated by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX), clearly showed different results. The different quantum chemical parameters were used to correlate the inhibition efficiency of the inhibitor and its molecular structure.