<p>Municipal solid waste incineration (MSWI) is increasingly being adopted in India for landfill diversion and energy recovery, but the management of MSWI fly ash (MIFA) remains constrained by limited region-specific data. Since MSWI ash in India is managed under an indirect regulatory framework, comparison with international benchmark criteria can help identify contaminants of concern (CoCs) and inform management decisions. This study is the first comprehensive characterization of fly ash collected from three MSWI facilities in Delhi across multiple seasons and evaluates its physicochemical properties, contaminant burden, and leaching behavior. Delhi fly ash (DFA) was fine-grained, strongly alkaline, and enriched in soluble salts and trace metal(loid)s relative to Delhi silt and coal fly ash, indicating that it should not be treated as equivalent to these fine-grained reference materials. TCLP results identified Cd as the only contaminant exceeding the selected TCLP-based benchmarks. In contrast, EN 12457–2 results showed broader leaching concerns, with soluble salts and selected trace metal(loid)s exceeding EU landfill acceptance limits. Chloride and TDS exceeded EU hazardous waste landfill acceptance limits in multiple samples, indicating that untreated DFA may require pretreatment or controlled management before landfill disposal. Combined ash leaching illustrated that adding DFA to bottom ash increased the leaching burden of the combined material, and none of the combined ash samples satisfied the selected reuse criteria. The findings highlight the need for separate leaching-based evaluation of fly ash and bottom ash before co-disposal, reuse, or treatment decisions, and support the development of India-specific MSWI fly ash management criteria.</p> Graphical abstract <p></p>