Problematic soils have always piqued the curiosity of geotechnical engineers. In this study, waste asphalt has been investigated as an environmentally acceptable stabiliser for collapsible soil. Compaction properties, collapse index, and California bearing ratio (CBR) were measured before and after treatment to see how well collapsible soil mixed with waste asphalt. Fourier transform infrared spectroscopy and X-ray diffraction examinations were utilised to examine the impact of the additions on the microstructure of the soil. The waste asphalt was added to the soil in proportions of (10, 30, and 50)%. Results indicate that waste asphalt is an effective sustainable stabiliser, with a 50% addition achieving a substantial reduction in the collapse index of nearly 70.76%. This is attributed to the waste asphalt coating the collapsible soil particles, and thus, isolating them from being subjected to the effect of water. Results have also shown that while the moisture content, liquid limit, plastic limit, and plasticity index diminished, the maximum dry density, shear strength, cohesion increased, and CBR values ameliorated with augmenting waste asphalt concentration. It may be concluded that subgrade, sub-base, and base are suitable pavement layers for incorporating waste asphalt at a composition of up to 50%.