The electronic and magnetic properties of oxygen- and sulfur-passivated one-dimensional armchair GaN nanoribbons (A-GaNNRs) are revealed using both firstprinciples density-functional theory and ab initio molecular dynamics simulations. We explore that an applied external electric field can further modulate the electronic properties of both pristine and passivated A-GaNNRs, thus changing their properties (semiconducting−metallic−half-metallic). A-GaNNRs of 0.9−3.1 nm width are subjected to further investigations, which reveal that sulfur termination transforms pristine A-GaNNRs from direct into indirect band gap semiconductors, without affecting their nonmagnetic nature. On the other hand, oxygen passivation introduces spin-polarized behavior with a finite magnetic moment. Magnetism characteristics in both bare and sulfur-passivated AGaNNRs are induced by applying a critical electric field along the direction of NR width. The passivated A-GaNNRs are more stable compared to bare ones, while sulfur-passivated A-GaNNRs exhibit higher stability at higher temperatures (>500 °C). Thus, our results suggest that A-GaNNRs can be used in a broad range of electronic, optoelectronic, and spintronic applications.