<p>Oxygen vacancies are regarded as crucial defects greatly affecting the electronic and optical properties of oxide films and devices, yet systematic studies on <i>κ</i>-Ga₂O₃ are still lacking. Herein, we investigate the thermodynamic, electronic, and optical properties of oxygen vacancies in <i>κ</i>-Ga₂O₃ using density functional theory calculations with the hybrid functional. The electronic structure reveals that oxygen vacancies create a deep donor defect in the bandgap, with defect levels and transition energies influenced by Ga atom displacement and localized electron dynamics. This interplay explains the stability of vacancies at specific sites and their connection to experimentally observed defect levels. Additionally, oxygen vacancies generate distinct absorption and electron energy loss peaks in the ultraviolet range. Our results elucidate the nature of oxygen vacancies, and offering a foundation for tuning and optimizing the electrical and optical properties of <i>κ</i>-Ga₂O₃ films and improving device performance through defect engineering.</p><p></p>