This study investigates the influence of incinerated biomedical waste ash (IBMWA) on the properties of cement-treated road base materials (CTRB). IBMWA, a by-product of high-temperature (850–1100 °C) incineration of biomedical waste, contains inorganic components that could potentially enhance or modify the characteristics of road construction materials when used as a partial replacement for cement. CTRB was prepared by replacing OPC with 0%, 20%, 40%, 60%, 80%, and 100% IBMWA in order to determine the recommended maximum dosage of IBMWA, without compromising its effectiveness. The laboratory performance of CTRB with IBMWA was assessed, which includes unconfined compressive strength (UCS), indirect tensile strength (IDTS), resilient modulus (MR), and wetting and drying (W-D) resistance. The research results demonstrated that the incorporation of IBMWA had a positive influence on the characterization of CTRB. The strength characteristics of CTRB containing IBMWA increased with an increase in curing time. However, the strength of CTRB decreased with the increase of IBMWA content. The 7 days UCS of CTRB containing 20% IBMWA met the specification of base course as set by IRC: 37–2018. Additionally, after 12 cycles of wetting and drying, considered mixtures exhibited weight loss below the thresholds established by IRC: 89–2018. The concentrations of heavy metals in these mixtures remained below the limit set by the United States Environmental Protection Agency (US EPA) standards. Thus, partially replacing OPC with IBMWA in CTRB can mitigate heavy metal leaching issues, with 20% IBMWA identified as the suggested maximum dosage for effective performance.