Very recently, two R3−c Dirac half-metal materials, LaMnO3 and MnF3, were found and investigated by Du et al. via first principles. They stated that these types of materials with half-metallic band structures and multiple linear band dispersions might exhibit excellent 100% spin polarization and ultrafast electron transport. However, the application of MnF3 material in the field of spintronics is limited owing to its low Curie temperature (Tc). In this work, we proposed a new half-metal material—MnBO3. This material satisfies two demands at the same time—it is a half-metal with a high Tc, and it has multiple nearly linear band crossings. The effects of the uniform strain, vacancies, spin–orbit coupling, as well as hole and electron doping on its electronic structures have been discussed in detail. Furthermore, to better study its specific behaviors under extreme conditions, such as high temperature or pressure, we also investigated the thermodynamic properties of MnBO3 through the quasi-harmonic Debye model. Finally, its thermal stability at room temperature has been proved in this article by means of ab initio molecular dynamics (AIMD) simulations. We hope that MnBO3 can attract more attention for R3−c-type half-metallic materials with linear band crossings and a high Curie temperature in experimental and theoretical areas.