<p>Expansive soils are documented for their tendency to upheave, pose substantial challenges to infrastructure integrity, particularly adverse swelling behaviour. Traditional solutions involving lime and cement treatments are prolong considered as more effective, however it raises the severe environmental impacts. This study introduces an alternative and environmentally friendly xanthan gum (XG) biopolymer as a bio-stabilizer to counteract soil swelling. An experimental investigation was conducted on two distinctive types of expansive soils treated with varied XG concentrations (0.5%, 1%, 1.5%, and 2% on dry weight basis). The impact of XG treatment on swelling behaviour was systematically evaluated through series of swell-compression tests using consolidation apparatus. The test results underscore the efficacy of a XG concentration, demonstrating a significant reduction of both percent swell and swell pressure, in comparison with untreated soils. The reduction mechanism was found as XG-treated soil inducing a gel-like structure, boosting cohesion, and mitigating soil dispersion through pore filling and particle bonding process, that help to reduce the accumulated swelling strain. Microscopic analysis using scanning electron microscope (SEM) images and Fourier-transform infrared spectroscopy (FTIR) were used as additional insights, which confirms the formation of distinct gel-like structure, obstructs void spaces, impedes water drainage, and augments overall soil stability within the XG-treated soil matrix. Further, the mechanism of observed decrease in swelling tendencies of XG-treated soil is explained with the help of soil-biopolymer interaction.</p>