Graphene nanoribbons hold great promise for next-generation nanoscale semiconductor devices, yet their performance in radiation environments is critically compromised by displacement damage caused by high-energy particles. In this work, we employ the non-equilibrium Green’ s function formalism combined with a tight-binding model to systematically investigate how irradiation-induced monovacancy defects influence the transport characteristics of armchair-edged GNRFET. We compute current–voltage characteristics under varying gate and drain–source biases for devices containing 0, 2, 5, and 10 randomly distributed vacancies, and further compare the effects of two distinct spatial configurations at identical defect concentrations: one in which vacancies are randomly dispersed throughout the ribbon and another in which they form aggregated clusters. Complementary analysis of the PLDOS provides microscopic insight into the electronic origins of transport degradation. Our results show that vacancy defects break the translational symmetry of the nanoribbon lattice, introduce structural disorder, and trigger Anderson localization. As the number of defects increases, the ON-state current drops sharply, the ON/OFF ratio deteriorates significantly, and the switching functionality is severely suppressed. PLDOS maps confirm the emergence of localized electronic states near the Fermi level, directly linking spatial disorder to conductance collapse. Beyond a critical disorder threshold, the rate of performance degradation slows significantly, indicating saturation of the localization effect. Most importantly, aggregated defects cause substantially less degradation than randomly distributed ones at the same concentration: PLDOS reveals that clustered vacancies confine electronic perturbations to localized regions, preserving extended conducting pathways elsewhere in the ribbon, whereas random vacancies induce pervasive state localization across the entire channel. This study establishes that the spatial distribution of defects, rather than merely their number, is a decisive factor governing radiation tolerance in GNRFET.