This study investigates the effects of two different parameters on the mechanical properties of carbon fiber-epoxy composites. The two addressed parameters are the composite’s exposure to gamma radiation with different doses, and the incorporation of lead nanoparticles with different weight percentages in the epoxy matrix. Unidirectional carbon fiber-epoxy composites are manufactured using the hand layup vacuum bagging process, and they are characterized by tensile tests and scanning electron microscope. The first part of the study entails fabricating composite laminates with different weight percentages of lead nanoparticles, namely, 0wt%, 1wt%, 2wt%, 3wt%, 4wt% and 5wt%. The results show that composites incorporating lead nanoparticles up to 3wt% exhibit monotonically improved tensile strength and Young’s modulus without compromising their ductility. Whereas, degradation of these mechanical properties is observed with increasing lead content beyond 3wt%. For the second part of the study, composite specimens are exposed to different doses of gamma radiation, namely, 0, 25, 50, 75 and 100 kGy. It is observed that the tensile strength, the modulus of toughness and the ductility of the composites improve for radiation exposures up to 25 kGy. However, radiation exposures higher than 25 kGy lead to deterioration in the tensile strength, modulus of toughness and Young’s modulus with negligible effect on the ductility.