The utilization of alternative materials in pavement construction offers environmental and economic benefits. One such alternative material is industrial waste plastic dust (IWPD) derived from high-density polyethylene (HDPE), which can enhance the rheological performance of bitumen to withstand the challenges posed by increasing traffic volumes worldwide. This study investigates the effects of incorporating IWPD into bitumen at various percentages (3%, 6%, and 9% by weight of the optimum bitumen content) on the physical, rheological, and morphological properties of IWPD-modified binders, as well as the moisture susceptibility of asphalt mixtures containing these binders. The penetration, softening point, rotational viscosities, rutting factor, and fatigue resistance of the IWPD-modified bitumen blends are evaluated using methods such as dynamic shear rheometer, short- and long-term aging tests using the rolling thin film oven (RTFO) and pressure aging vessel (PAV). The results indicate that the modified bitumen blends enhance the properties of the neat bitumen. Particularly, the blends with 6% and 9% IWPD content exhibit optimal performance in terms of increased rutting and fatigue resistance, as well as improved moisture susceptibility of hot mix asphalt (HMA). However, the 6% IWPD content is considered the most suitable due to better miscibility compared to the 9% content, which exhibited phase separation as observed in the scanning electron microscopy (SEM) results. These findings contribute to a better understanding of the impact of plastic fines as bitumen modifiers on the rheological and performance characteristics of HMA, offering insights into sustainable practices for pavement construction.