We have studied the structural, electronic, magnetic, thermoelectric and optical properties of the half-metal BaRuO₃ using the accurate full-potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). The generalized gradient approximation (GGA) was used to treat the exchange and correlation potential. The GGA approximation was also used to enhance the description of the electronic structure after calculating theoretically the Coulomb repulsion (eV). The ferromagnetic (FM) phase of BaRuO₃ is more stable. This result is in accordance with experimental and theoretical calculations. The calculated magnetic moments in BaRuO₃ were found to arise especially from the Ru-4d state electrons. We have obtained the semiconductor gap (0.9eV) in spin-up while in spin down, the metal character was dominant, and therefore BaRuO₃ has a half-metallic behavior. The thermoelectric efficiency was 0.12 at room temperature. Here we have considered only the electronic thermal conductivity, we have not included the lattice thermal conductivity. The relaxation time was assumed constant. The approximation was also used to analyze the optical properties by determining the complex dielectric function from which are derived the other parameters.