<p>The development of high permittivity materials is the key to enhancing the performance of energy storage devices and promoting the application of new energy. In recent years, the colossal permittivity properties of donor–acceptor co-doped rutile TiO₂ ceramics have been widely studied. While the breakdown field strength of A⁵⁺–B³⁺ co-doped TiO₂ ceramics is relatively low, limiting their energy storage applications and presenting a critical bottleneck that needs to be urgently overcome. In this study, Fe³⁺ was incorporated into (Ta⁵⁺ + La³⁺) co-doped TiO₂ ceramics to explore the effects of dual acceptor co-doping with a significant difference in ionic radii on the dielectric properties and high-field conduction behavior of the co-doped ceramic system. The results show that the Fe³⁺ incorporation effectively stabilizes the dielectric properties under bias, particularly with respect to comprehensive performance factors such as DC bias voltage and frequency stability. However, at relatively high contents, Fe³⁺ ions lead to a deterioration of the dielectric properties in the co-doped ceramics.</p>