The depletion of crude oil reserves has spurred the search for alternative resources for road construction. The use of waste engine oil (WEO) in asphalt binders and mixtures is investigated in this study, focusing on the performance of WEO-modified mixtures and their possible advantages for the environment and the economy. This study evaluates the effects of WEO at four replacement levels: 0.2%, 0.4%, 0.6%, and 0.8% by weight of bitumen. The primary goals are to measure the mechanical performance of asphalt mixtures containing WEO, determine the ideal WEO percentage, and evaluate the physical characteristics of a binder modified with WEO. The methodology includes evaluating the performance of the asphalt mixture, the properties of the binder and aggregates, and determining the optimum bitumen content (OBC). Key tests conducted in this study are the Marshall Stability and Flow tests for the asphalt mixture, the Penetration and Softening Point tests for binder characterization, and the Los Angeles Abrasion and Aggregate Crushing Value tests for assessing aggregate quality. The findings show that although WEO can affect asphalt performance, the right balance is crucial. At 0.2% WEO, the asphalt mixture achieved the highest Marshall Stability (17.71 kN) and acceptable flow value (3.1 mm), indicating improved durability and flexibility. Although, higher WEO content softens the binder further, it compromises mechanical strength. Higher WEO content led to lower stiffness and reduced load-bearing capacity. To support Malaysia's sustainable infrastructure and environmental preservation, this study attempts to optimize WEO usage. Thus, 0.2% WEO is recommended as the optimum dosage for modified bitumen to achieve enhanced pavement performance while promoting recycling of hazardous waste.