Kenaf–cenosphere hybrid epoxy composites were fabricated using hand lay-up followed by compression molding to investigate the effect of waste-derived hollow cenospheres on the physical, mechanical, lightweighting, and sustainability characteristics of natural fiber-reinforced composites for mobility applications. Composites were prepared with constant kenaf fiber content (35 wt.%) and varying cenosphere content from 0–15 wt.%: C1 (0 wt.%), C2 (5 wt.%), C3 (10 wt.%), and C4 (15 wt.%), with epoxy content adjusted accordingly. Increasing cenosphere content reduced theoretical density from 1.28 to 1.22 g/cm³ and decreased actual density by 6.5%, while void content increased from 3.9% to 5.7%. Water absorption decreased by 26.2%, indicating improved moisture resistance. Mechanical analysis showed that tensile and flexural strengths reached maximum values of 45.6 MPa and 88.9 MPa for C3, representing improvements of 39% and 13.2%, respectively, over the control composite. Impact strength increased continuously, reaching 15.6 kJ/m² for C4, corresponding to a 59.2% enhancement. Lightweighting analysis demonstrated significant weight reductions of 84.33–85.35% relative to mild steel and 54.44–57.41% compared to aluminum. Sustainability assessment indicated improved environmental performance with increasing cenosphere content due to higher industrial waste utilization, reduced epoxy dependence, and renewable kenaf incorporation, yielding a ranking of C4 > C3 > C2 > C1. SEM analysis revealed improved fiber–matrix adhesion for C3 and enhanced crack branching in C4. TOPSIS analysis ranked C3 and C4 as the most preferred configurations (relative closeness = 0.59). Overall, C3 provided the best balance between mechanical performance, lightweighting, cost efficiency, and sustainability, while C4 was more suitable for impact-resistant applications.