The current study aims to improve free swell, swell pressure, cohesion (C), and internal friction angle (θ) of expansive soil using Bagasse Ash (BA) and Polypropylene Fibre (PPF) with varying percentages. The properties of untreated and treated soil were determined by the one-dimensional consolidation test and the unconsolidated undrained (UU) triaxial compression test. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy-dispersive spectroscopy (EDS) analysis.  The results showed that the addition of BA in untreated soil decreased the free swell, swell pressure, and cohesion (C) by 64.86%, 61.54%, and 20.90%, respectively, and increased the internal friction angle by 47.19%. The test results further revealed that the inclusion of 20% BA and 1% PPF in untreated soil decreased the free swell, swell pressure, and C by 78.38%, 76.92%, and 45.45%, respectively, while increasing the internal friction angle by 57.09%. The test results of untreated soil indicated illite, kaolinite, montmorillonite, and non-clay minerals, predominantly quartz. Moreover, the XRD result of the treated soil showed the reduction of montmorillonite content. Further variation in the behavior of treated soil was confirmed using SEM and EDS analyses. These results would provide a deep understanding of the optimum contents of BA and PPF for treating the expansive soils to address the potential hazards in the construction.