<p>This study presents a comprehensive theoretical investigation into the structural, elastic, electronic, magnetic, optical, and thermoelectric properties of the double perovskite oxide La₂MnRuO₆, conducted using first-principles density functional theory (DFT). Our calculations predict that the ground state of La₂MnRuO₆ is a ferromagnetically ordered cubic structure with the Fm-3&#xa0;m space group. This structure is found to be thermodynamically stable, as confirmed by its negative formation energy, and mechanically stable, as verified by the calculated elastic constants satisfying the Born-Huang criteria. The electronic structure calculations, performed using the modified Becke-Johnson (mBJ) potential, reveal a compelling half-metallic character. The material is metallic in the spin-down channel, while exhibiting a semiconducting gap in the spin-up channel. This half-metallicity is corroborated by the calculation of an integer total magnetic moment of 7.00 μ_B per formula unit. The analysis of its mechanical properties indicates a ductile and elastically anisotropic nature. Optical properties suggest significant absorption in the ultraviolet region, making it a candidate for UV-based optoelectronic devices. Furthermore, the thermoelectric properties show a high Seebeck coefficient and a substantial power factor at elevated temperatures, indicating potential for energy harvesting applications. The unique spin-dependent transport characteristics suggest La₂MnRuO₆ as a promising multifunctional material for advanced spintronic devices and potential high-temperature thermoelectric energy harvesting applications.</p>