A new heterocyclic Schiff base, 4-(1-(4-(dimethylamino)benzyl)-5-methyl-1H-benzo[d]imidazol-2-yl)-N, N-dimethylaniline (L), has been synthesized and characterized. The molecular structure of compound L was confirmed by 1H NMR, FT-IR, UV-Vis and elemental analysis. The performance and inhibition mechanism of compound L against the corrosion of carbon steel in 1 M HCl and 0.5 M H2SO4 were studied by weight loss method, Tafel polarisation and electrochemical impedance spectroscopy (EIS). The compound behaves as a mixed-type inhibitor and obeys the Langmuir adsorption isotherm. The morphological appearance of compound L on the carbon steel surface by scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirmed that compound L was adsorbed on the carbon steel to form a film. The thermodynamic parameters were calculated and discussed. Quantum chemical parameters were also determined. This study confirms the agreement between the experimental and theoretical results.