A huge amount of incineration ash is generated daily from municipal solid waste (MSW) incineration plants worldwide. In Singapore, most of the incineration ash is disposed at Semakau Landfill, whose capacity cannot meet our increasing demand of waste disposal. This study reports a method to use MSW Incineration Bottom Ash (IBA) as a partial replacement of the ordinary Portland cement in deep cement mixing for soil improvement. We investigate the geotechnical and leaching properties of soil-cement-IBA mixes and assess the toxic element concentrations in dry mixes and groundwater. Our results show that this method is feasible in terms of uniaxial compressive strength, leaching concentrations of heavy metals and other elements, as well as estimated toxic element concentrations in dry mixes and groundwater. The partial replacement of the cement with IBA slightly reduces the short-term strength of the IBA and cement treated soil but slightly improves the long-term strength. The heavy metals can be immobilized effectively in the solidified soil-cement matrix. The reduction in the short-term strength is due to an increase in total porosity with higher IBA content, while the growth in the long-term strength is related to an increase in gel porosity associated with hydration reaction. This method is possible to offer an alternative safe IBA disposal and meanwhile to reduce the dependence on imported cement in resource scarce countries (like Singapore).