All-inorganic CsPbI3 halide perovskite has become a hot research topic for applications in next-generation optoelectronic devices. However, the main limitations are the high-temperature synthesis and poor phase stability. In this study, we demonstrate a unique solution-phase strategy for the low-temperature preparation of black-phase CsPbI3 by in situ electrochemistry. By controllable adjustment of the electrochemical growth process, annealing-free black-phase CsPbI3 can be synthesized. The black-phase CsPbI3 showed high-purity red photoluminescence at approximately 690 nm with ultra-high environmental stability for up to 11 days at a high relative humidity of 70%. The underlying mechanisms of the formation of the highly stable black-phase CsPbI3 at room temperature have been discussed in this study. The results provide a new platform for the large scale, low-temperature, and convenient synthesis of black-phase CsPbI3 perovskite.