Incineration of municipal solid waste (MSW) along with energy recovery has been proven to reduce the volume of waste destined for landfills by as much as 90%. According to Indian solid waste management regulations, all municipal solid waste must be treated in composting facilities, waste-to-energy facilities, or other processing plants before being disposed of in landfills. This requirement not only lessens the spatial footprint of landfills but also contributes positively toward environmental sustainability. However, one challenge that remains is how to effectively reuse or dispose of the residues left behind after the incineration process. Even with comprehensive resource recovery, current estimates indicate that 25–35% of total MSW generated remains as residue that accumulates in landfills if not further used. Therefore, this research focuses on exploring the potential application of incinerated MSW ash as landfill liners. The study undertakes a meticulous analysis of both bottom ash and fly ash through extensive geotechnical characterizations. In order to gauge their suitability as landfill liners, the study conducts detailed geotechnical analysis on various aspects such as hydraulic conductivity and compressibility. Ultimately, this research promotes the massive utility of incinerated MSW ash, thereby encouraging a sustainable approach toward landfill management.