Nowadays, a properly designed corrosion protection system, which is essential for large-scale practical application remains a big challenge. Herein, we report a combined experimental and theoretical study of the adsorption of a galactomannan polysaccharide, namely, Fenugreek gum (FG) on the mild steel (MS) surface in 1.0 M HCl by using electrochemical techniques, X-ray photoelectron spectroscopy (XPS), DFT, molecular dynamic (MD) simulations, radial distribution function (RDF) and mean square displacement (MSD). XPS results show that the FG forms a layer on steel surface. FG adsorption onto the steel surface was found to follow Langmuir model. The electrochemical results demonstrated that FG acts as mixed-type inhibitor. Scanning electron microscope (SEM) was used to examine the surface morphology of the samples. Our findings provide deeper insights into understanding the interaction mechanisms of FG with MS and can be helpful to explore novel approaches to mitigate the steel dissolution occurring at the acidic environment.