This study aimed to examine the impact of graphite morphology on the water absorption and fatigue properties of biopolyamide-based composites. Graphite was incorporated into the polymer matrix in two distinct forms—flake and expanded—to evaluate its effect on key performance characteristics beyond the traditionally examined tribological effects. Flake graphite has thin, flat flakes with layered crystalline structure, high purity, good crystallinity, and high thermal/electrical conductivity. It is chemically stable and lubricating, used in lubricants, refractories, batteries, and pencils, and as precursor to expanded graphite. Expanded graphite is processed by intercalating flake graphite with acids then rapidly heating to create a worm-like, porous structure. It has low density, high surface area, thermal stability and conductivity, and forms flexible sheets. Uses include thermal management, fire-resistant materials and electrodes in batteries. A comprehensive experimental methodology was employed, encompassing density measurements, water absorption tests, and mechanical assessments such as static tension, bending, and impact resistance. Fatigue behavior was assessed using the Lehr method, and mechanical hysteresis loops were analyzed to characterize viscoelastic behavior. Additionally, surface topography, wear mechanisms, and tribological performance were investigated. The inclusion of graphite significantly enhanced the composite performance. Water absorption was reduced by up to 20%, primarily due to the tortuous path effect created by the lamellar structure of graphite and improved filler–matrix interactions. Flake graphite composites exhibited increased fatigue and dynamic creep resistance, as confirmed by hysteresis analysis and cyclic loading tests. The surface topography of expanded graphite samples was found to influence friction behavior, particularly under low-load conditions. Furthermore, graphite-filled composites maintained their mechanical properties after accelerated thermal aging, in contrast to neat BioPA, which exhibited significant degradation. These findings underscore the critical role of graphite morphology in tailoring not only the tribological but also the moisture and fatigue resistance of bio-based composites, thereby opening new avenues for sustainable material design.