<p>The use of agricultural waste ash (AWA) as an alternative filler in asphalt mixtures has attracted attention for its potential to enhance sustainability while reducing reliance on conventional materials. This review summarises recent developments in the processing of agricultural residues into AWA, their physical and chemical characteristics, and their performance as fillers in asphalt mixtures. Existing studies have largely focused on rutting, fatigue, and moisture resistance, while other important aspects such as ageing, thermal cracking, freeze–thaw durability, and long-term field performance remain insufficiently explored. The review also highlights environmental and economic considerations, including the need for comprehensive life-cycle assessments and techno-economic analyses to evaluate feasibility. Despite encouraging laboratory findings, pilot- and full-scale trials are limited, and standardised specifications for the use of AWA are lacking. The paper identifies key research gaps and outlines priorities for future work, emphasising that while AWA shows strong potential as a sustainable filler, further systematic studies are required for widespread practical adoption.</p>