Two-dimensional materials and their multilayers or heterostructures are promising candidates for optoelectronic devices. Their performance such as the transient current can be remarkably modified under irradiation since the atoms are extremely exposed. This effect, however, still lacks theoretical understanding. Using real-time time-dependent density functional theory extended to open systems for electrons and Ehrenfest dynamics for the moving ion, we explore the single-ion irradiation effects on graphene electronics. Perturbed electronic transport is identified in a field-effect transistor setup. The peak transient current is calculated as the key indicator to quantify the irradiation effects, the irradiation-energy dependence of which shows distinction from the stopping power that was well understood in recent studies. We find that the perturbation in transient current is driven by delocalized plasmonic excitation, in contrast to the localized electronic excitation that has a strong impact on the stopping power. The site dependence of transient current is determined by the local electron density and ionic charge, which highlights the roles of the lattice and electronic structures of materials. Following these understandings and the database developed for typical space-irradiation conditions, the device responses of graphene nanoelectronics can be modeled. These results and methods lay the ground for the material-informed design of nanoelectronics in, for example, space applications.