Defect engineering is considered as one of the most efficient strategies to regulate the electronic structure of materials and involves the manipulation of the types, concentrations, and spatial distributions of defects, resulting in unprecedented properties. It is shown that a single‐layered MnO2 nanosheet with vacancies is a robust half‐metal, which was confirmed by theoretical calculations, whereas vacancy‐free single‐layered MnO2 is a typical semiconductor. The half‐metallicity of the single‐layered MnO2 nanosheet can be observed for a wide range of vacancy concentrations and even in the co‐presence of Mn and O vacancies. This work enables the development of half‐metals by defect engineering of well‐established low‐dimensional materials, which may be used for the design of next‐generation paper‐like spintronics. A manganese dioxide monolayer was rendered half‐metallic by a defect engineering strategy, which was confirmed by calculations. These theoretical studies showed that the half‐metallicity of a single‐layered MnO2 nanosheet can be observed for a wide range of vacancy concentrations and even in the presence of both Mn and O vacancies.