High surface friction and lack of antibacterial properties limit the efficiency of fixed metallic orthodontic appliances. Graphene oxide/silver (GO/nAg) nanocomposite coatings were constructed on the surface of a representative nickel–titanium (NiTi) alloy using different sizes of GO via pulse electrodeposition; these coatings were characterized in terms of their microstructure, surface properties, and related biological features. Small-sized GO (SGO) with a lateral size of about 70 nm had more sites for nAg to bind, which helped to form serried and uniformly dispersed nAg; this decreased the coefficient of friction to 0.1, reduced the corrosion current density by ten times, and decreased the amount of corrosive ions, as determined from electrochemical and stress corrosion tests. In the coating containing large-sized GO (LGO), the prolonged growth of nAg resulted in a larger size and scattered distribution, thus having limited optimization in terms of friction and corrosion resistance. Both GO/nAg coatings were biocompatible with L929 cells and adhesion to human gingival fibroblast cells. The LGO/nAg coating released two folds of Ag⁺ than the SGO/nAg coating initially, while the latter exerted a stable antibacterial effect over seven days against 90% Streptococcus mutans through sustained release. It is suggested that the size of GO could regulate the mechanical and biological properties of GO/nAg coatings. This study aims to improve the efficiency of orthodontic treatment and promote the clinical popularization of multifunctional GO/nAg nanocomposite coatings in the oral environment.