Utilizing natural fillers as reinforcement in polymer composites is an effective way of producing environmentally friendly and sustainable engineering materials. In this study, polyester composites reinforced with 5–20 wt% Artabotrys hexapetalus fruit peel particles were fabricated and evaluated for their mechanical, free vibration, thermal, and water absorption properties. Furthermore, the morphology, crystalline phases, and functional groups of the particles were also examined. The composite with 10 wt% filler had the best mechanical properties, with a tensile strength of 33.44 MPa, flexural strength of 56.76 MPa, and an impact strength of 7.16 kJ/m2. Free vibration analysis indicated that the composite with 15 wt% reinforcement demonstrated the highest natural frequency of 26.84 Hz, due to its increased stiffness. The thermal stability of composites was studied using thermogravimetric analysis and differential thermogravimetric analysis. The composites reinforced with 15 wt% filler recorded better thermal stability at higher temperatures. Furthermore, the hydrophilic nature of composites increased with increase in filler quantity. As a result, the composite incorporated with 20 wt% showed the highest water absorption rate with an increased diffusion rate of 0.099 × 10−10 m2/s and water contact angle of 51.5°. The failure mechanism of the composites was investigated using scanning electron microscopy. These findings highlight the feasibility of Artabotrys hexapetalus fruit peel particles as a cost-efficient and environmentally sustainable reinforcement for polymer composites, facilitating the development of lightweight structural materials with a focus on sustainability.