The effects of γ-ray and electron irradiation on the microstructural evolution and mechanical properties of SnPb eutectic solder joints were investigated. Following electron irradiation, the SnO₂ phase induced by γ-ray irradiation transformed into β-Sn, and the dislocation density in the β-Sn crystal decreased. Moreover, numerous point defect clusters formed in the β-Sn crystal, some of which transformed into an amorphous phase, increasing the amorphous layer thickness. Meanwhile, electron irradiation likewise resulted in rotation of the (220) plane of β-Sn nanograins and reduction of SnO₂ in the β-Sn crystal. Additionally, upon exposure to γ-ray and electron irradiation, the average shear strength of the solder balls was initially increased by 10.10%, followed by a decrease of 3.53% and 4.77%, respectively. The plasticity and the dimple count on the fracture surfaces of the solder joint initially decreased but subsequently increased.