Incineration of municipal solid waste is increasingly being adopted in developing countries from the past couple of decades as a waste management strategy. This is driven by rapid urbanization, population growth and scarcity of land for landfills. MSW incineration reduces the volume of waste by 70–90% but still leaves behind substantial quantities of residual ash for disposal. Managing and disposing ash safely adds significant costs over just burning the waste, undermining the economics of incineration. The present study explores the potential applications of municipal solid waste incinerated (MSWI) ash as a landfill liner. This study provides a comprehensive characterization of both fresh and aged incinerated MSW ash (fly ash and bottom ash) collected from waste to energy plant (WTE). Analyzing the physicochemical properties of incinerated ash incorporating its mineralogy, morphology, and chemical composition is essential for its effective application in geotechnical engineering. This approach offers a sustainable alternative to traditional liner materials.