An energetic-material (NaN₃) deflagration method for preparing N- and Ti³⁺-codoped TiO₂ nanosheets (NT–TiO₂) was developed. In this method, N radicals filled the crystal lattice, and Na clusters captured partial O from TiO₂. The deflagration process was fast and facile and can be completed within < 1 s after ignition. The obtained NT–TiO₂ exhibited rough surfaces with nanopits and nanoholes. The doping concentration can be regulated by controlling the NaN₃ addition. The NT–TiO₂ samples showed significant enhancements in the visible-light absorption and photoelectric response. The simultaneously produced N radicals and Na clusters from NaN₃ deflagration served as N sources and reduction agents, respectively. Additionally, the high deflagration temperature/pressure improved the reactivity of N radicals and Na clusters. Thus, the present NaN₃ deflagration method was demonstrated as an ultrafast and effective approach to fabricate NT–TiO₂ with a visible-light response. The proposed NaN₃ deflagration method allows the ultrafast synthesis of new functional materials via the efficient deflagration of energetic materials.