Bagasse ash (BA), a by-product of the sugarcane industry, is produced in substantial amounts and typically discarded, leading to environmental degradation and the misuse of valuable agricultural land. While BA has shown potential as a filler in asphalt concrete, limited research exists, particularly in Pakistan, regarding its effects on the stability and flow characteristics of asphalt mixtures. This study addresses this research gap by investigating the impact of varying proportions of locally sourced BA on asphalt concrete performance. Key material properties, such as surface texture and chemical composition, were analyzed using techniques like Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDX), and Fourier Transform Infrared Spectroscopy (FTIR). The study was conducted in two phases: initially, asphalt mixtures with filler contents of 3%, 4.5%, and 6% were tested; subsequently, BA was used to replace these fillers at rates of 10%, 20%, and 100%. Marshall tests were performed to measure stability, flow, and the Marshall quotient, alongside an evaluation of volumetric properties such as air voids (Va), voids in the mineral aggregate (VMA), and voids filled with asphalt (VFA). The results indicated that replacing 20% of the filler with BA at 6% filler content achieved the highest Marshall stability, recorded at 16.1 kN. These findings suggest that BA can be a viable and sustainable alternative filler in asphalt concrete, with optimal performance observed at the 20% replacement level.