The present study utilizes first-principles calculations grounded in density-functional theory (DFT) to examine the thermoelectric, electronic, elastic, optical, and structural properties of BiGaIn2S6. It is demonstrated that the approximated structural parameters (a, b, c, β, c/a, b/a), as well as atomic sites, correspond to the experimental data. Based on the measured elastic properties, it can be concluded that the investigated material possesses anisotropy and ductility. The computation of the electronic properties of our compound unveiled its semiconducting characteristics. The mBJ-LDA method was employed to ascertain that the compound exhibits an indirect band gap (Γ→Γ-E) of 2.711 eV. Based on the computational outcomes, it can be concluded that the real part of dielectric complex and refractive index exhibit a degree of anisotropy. The compound exhibits promising potential for optoelectronic applications due to its tolerable values of optical properties such as optical conductivity, absorption aspect, refractive index, and reflectivity. The positive Seebeck coefficient obtained from the calculation indicates that this compound can be classified as a p-type material. The semiconductor BiGaIn2S6 exhibits a maximum ZT value of 0.98741 when the charge carrier concentration is increased to n = 0.14494 × 1022 cm−3 or when the chemical potential lowers to 0.47499 Ryd. The material being studied demonstrates potential uses in the fields of thermoelectric and optoelectronic devices.