In the present investigation, the corrosion inhibition property of the newly synthesized3-(4-chlorobenzoylmethyl)-1-methylbenzimidazoliumbromide ([BMMB]+ Br−)ionic liquid on carbon steel was investigated in 1 M HCl solution using electrochemical studies. Polarization study revealed that [BMMB]+ Br− is a mixed type of inhibitor. The impedance to metal dissolution was increased not only with increasing inhibitor concentration but also with temperature. The diminished current amplitude waves obtained in the electrochemical noise analysis (ENA) technique implied high noise resistances thereby indicating the formation of passive inhibitor layer. Adsorption of [BMMB]+ Br− ionic liquid on carbon steel was spontaneous and followed a Langmuir adsorption isotherm. The surface examination of the coupons before and after engrossed in inhibited medium was analyzed using Attenuated total reflectance – Fourier transform infrared spectroscopy (ATR-FTIR) and scanning electrochemical microscope with energy dispersive X-ray (SEM/EDX) studies and confirmed that the surface of carbon steel was protected from corrosion by the adsorption of [BMMB]+ Br− ionic liquid. Thermodynamic properties revealed that [BMMB]+ Br− has both physical and chemical adsorption behavior. In addition, density functional theory (DFT) calculations were carried out to give atomic level understandings to the experimental results by deducing the electronic properties of inhibitor in proportion to inhibition efficiency in aggressive medium.