Organic-inorganic hybrid halide perovskites have garnered significant attention as photovoltaic materials due to their exceptional solar cell performance and ease of fabrication. Nevertheless, their commercial viability remains hindered by poor stability and Pb-related toxicity. Quaternary thioiodides, defined by ns2 lone pair cations and robust metal-chalcogen bonds, exhibit favorable properties including suitable bandgaps, high permittivity, and enhanced stability. In this study, a novel quaternary thioiodide material, Ba2BiS2I3, aiming to overcome the stability and toxicity issues faced by lead-based perovskites, has been proposed. Employing first-principles calculations, it is determined that this material possesses an appropriate solar cell bandgap, high dielectric constant, low effective mass, and low exciton binding energy, showing potential as a new outstanding photovoltaic material. Moreover, our calculations indicate superior optical absorption properties for this material. Notably, the theoretical spectroscopic limit for maximal efficiency of Ba2BiS2I3 exceeds 28%. This investigation establishes the potential of lead-free quaternary thioiodides in advancing photovoltaic technology.