The improper disposal method of the agro-waste and currently followed practice of carbon-intensive open-field burning causes severe environmental pollution. Hence, it is essential to identify efficient ways of utilising these agro-residues. However, the absence of proper understanding of their characterisation and processing method hinders the acceptance of the agro-residual ashes in the cement industry. Although the pozzolanic performance of several agro-waste ashes is evidently reported in the earlier studies, a comprehensive review of the processing methods to be adopted for different agro-waste ashes is highly limited. Hence, the present review mainly focuses on the influence of different processing methods such as grinding, burning, chemical, thermomechanical and thermochemical on the pozzolanic performance of agro-waste ashes. The effect of different processing methods on physical, chemical, and mineralogical characteristics of agro-waste ashes such as rice husk ash, sugarcane bagasse ash, palm oil fuel ash, wheat straw ash, corn cob ash, corn stalk ash, rice straw ash, bamboo leaf ash, maize stalk leaf ash and elephant grass ash is presented. Moreover, variations in the fresh and hardened properties of concrete blended with the treated agro-waste ashes are discussed. It is observed from the review that the grinding of agro-waste ashes increases their pozzolanic activity index above 75\%, and subsequently, 10-50\% enhancement in the compressive strength is reported. Thermal processing improved the pozzolanic performance by decreasing the loss on ignition, and the optimum burning temperature of agro-waste ashes range from 500 to 700 degrees C. Furthermore, chemical treatment increased the specific surface area and decreased the loss on ignition of agro-waste ashes, thereby enhanced the strength and durability of blended cementitious systems. Moreover, synergistic use of processing methods is found to be efficient than respective individual processing methods. Based on a detailed review, it can be stated that the optimum conditions of processing to be adopted are diverse for different agro-wastes. The current study also presents the optimum parameters for the processing of different materials based on the extensive review. Therefore, by adopting an appropriate method of processing, the agrowaste ashes can be effectively utilised as supplementary cementitious materials.