Oxygen vacancies (VO) critically govern the electrical properties and operational stability of functional oxides. Conventional vacancy-healing strategies employ strong-bond dopants to statically suppress vacancy formation by strengthening metal-oxygen (M-O) bonds, but the incorporated dopants inevitably introduce substantial Coulomb scattering that degrades carrier mobility. Here, we demonstrate a transient volatile doping mechanism that dynamically heals VO-related defects while minimizing degradation of electron transport. In Ge-doped In2O3 (IGeO), Ge-O species contribute to the consumption of VO through an internal oxygen transfer process, thereby forming volatile GeO species that partially desorb from the host oxide. This transient process simultaneously enhances crystallization and suppresses deep-level defect states, enabling effective defect control with a low residual Ge concentration. The optimized IGeO thin-film transistors (TFTs) exhibit exceptional electrical stability with threshold-voltage shifts (ΔVth) of +0.01 and −0.11 V under positive and negative bias stress (±4 V), respectively, for 3600 s, while preserving a high field-effect mobility (μFE) of 62.7 cm2 V−1 s−1. Our findings establish transient volatile doping as a promising strategy for defect control in functional oxides.