Inhibition of mild steel corrosion by 2-methylbenzimidazole (MBI) in sterile enriched artificial seawater, and seawater with sulfate-reducing bacteria (SRB), was investigated using direct current polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). MBI was shown to be an effective inhibitor in controlling abiotic corrosion, and as well as microbiologically influenced corrosion (MIC) by two strains of SRB: Desulfovibrio desulfuricans and a local marine isolate (Desulfovibrio singaporenus). Tafel plots reveal that MBI predominantly controls the cathodic reaction. MBI is more effective in the inhibition of corrosion caused by D. desulfuricans than that caused by D. singaporenus. The corrosion inhibition effect of MBI on MIC is partially due to the inhibition of the bacterial activity. The adsorption of MBI on the mild steel surface follows a Langmuir adsorption isotherm model.