We firstly performed the reactive air wetting and brazing of Al₂O₃ ceramics using Ag–(0.5‒12)Nb₂O₅ fillers, where Nb₂O₅ can react with liquid Ag and O₂ from air to generate AgNbO₃. The contact angle of the Ag–Nb₂O₅/Al₂O₃ system almost linearly decreases from ~71.6° to 32.5° with the Nb₂O₅ content increasing, and the joint shear strength reaches the maximum of ~65.1 MPa while employing the Ag–4Nb₂O₅ filler, which are mainly related to the formation and distribution of the AgNbO₃ phase at the interface. Moreover, the interfacial bonding and electronic properties of related interfaces were investigated by first-principles calculations. The calculated works of adhesion (W_a) of Ag(111)/Ag–O–AgNbO₃(001) and AgNbO₃(001)/Al₂O₃(100) interfaces are higher than that of the Ag(111)/Al₂O₃(110) interface, indicating good reliability of the Ag/AgNbO₃/Al₂O₃ structure. The relatively large interfacial charge transfer indicates the formation of Ag–Ag, Al–O, and Ag–O bonds in the Ag/AgNbO₃/Al₂O₃ structure, which can contribute to the interfacial bonding.