Structural defects are central to the functionalities of materials. However, conventional approaches to defect control are often slow and imprecise. This work identifies and characterizes a distinct physical phenomenon of electrostructural bistability that provides a rapid and precise pathway for engineering materials with defect-controlled physical properties. A generalized theory of conductivity bistability is developed and experimentally validated to unify two distinct regimes: previously reported electrothermal bistability in weakly polarizable insulators, such as silicon, and electrostructural bistability in strongly polarizable materials, such as TiO₂. In agreement with the theory, experiments on TiO₂ demonstrate that bulk-homogeneous defect concentrations in electrostructurally bistable materials can be tuned rapidly and deterministically by controlling applied electric current. Abruptly interrupting the current quenches the system into long-lived, room-temperature metastable states with distinct properties. This establishes a practical, rapid, and scalable pathway for defect engineering with direct relevance to nonvolatile memory devices.