<p>Using density functional theory (DFT) with the GGA-PBESol, LDA, and TB-mBJ approximations, this paper thoroughly examines the structural, elastic, optoelectronic, and thermoelectric properties of chalcogenide-double perovskites Ba₂NbBiS₆ and Ba₂TaSbS₆, with the view to their potential use in optoelectronic and photovoltaic devices. Based on the calculation results, both compounds achieve the Born stability criteria and negative formation energy values, confirming their thermodynamic stability. Additionally, the elastic criteria analysis shows that the materials exhibit strong resistance to volume deformation while remaining ductile and demonstrate anisotropic characteristics, as seen through the ELATools software. Furthermore, the electronic band structure and density of states were investigated. The Ba₂NbBiS₆ compound exhibits an indirect band gap (L–X) of 1.58&#xa0;eV (mBJ-GGA) and 1.45&#xa0;eV (mBJ-LDA), while the Ba₂TaSbS₆ compound shows an indirect band gap (L–Γ) of 1.45&#xa0;eV (mBJ-GGA) and 1.28&#xa0;eV (mBJ-LDA). Analysis of the (DOS) and the electronic band structure revealed the contribution of 4d_Nd for Ba₂NbBiS₆ and 5d_Ta for Ba₂TaSbS₆. Furthermore, optical parameters derived from the dielectric function, including reflectivity, absorption coefficient, and refractive index were predicted. As a result, both compounds exhibit strong photon absorption extending from the visible to ultraviolet regions, with absorption coefficients of 342.03 × 10⁴/cm for Ba₂NbBiS₆ and 333.92 × 10⁴/cm for Ba₂TaSbS₆, indicating their high potential for optoelectronic devices. In addition, thermoelectric properties such as the Seebeck coefficient, electrical conductivity, thermal conductivity, ZT merit, and power factor were evaluated. The results provide valuable insights that may guide future experimental studies on these promising materials.</p>