The optical properties of doped SrTiO3 are crucial for solar energy conversion due to their correlation with their efficacy to absorb and convert sunlight to energy. In this study, the impact of La, Co, Cr, Sc, and Ir substitutions on the structural, optical, electrical, and photocatalytic properties of SrTiO3 were investigated by a series density functional theory (DFT) calculation. Analyses primarily initially focused on the effects of doping and co-doping with Lanthanum (La) followed by systematic investigations of the impact of transition metal (TM) doping with Scandium Chromium, Cobalt and Iridium (Sc, Cr, Co, Ir) an finally co-doping with La and the TM elements. Co-doping leads to a reduction in the bandgap energy and a shift in the bandgap region, making the material more suitable for photo-catalysis. Structures singly-substituted with La, Sc, Cr, Co, and Ir primarily absorbed light in the ultraviolet region, which limits their use in light-based devices. However, SrTiO₃ systems co-doped with La-Ir exhibited significant absorption in the visible region (∼400–750 nm). The co-doped SrTiO₃ maximizes solar light utilization, making it well-suited for applications such as solar cells. Our study sheds light into the optical properties of doped SrTiO₃, highlighting its potential for practical use in solar energy conversion.