In this work, first-principles calculations based on density functional theory are presented to explore the effect of plasmonic-metal doping on structural, electronic, and optical properties of Strontium Titanate (SrTiO₃). All the computations are performed on the ATK-VNL package with generalised-gradient approximation. The pristine SrTiO₃ is a wide band gap material and its absorption is limited to the ultra-violate region only. Therefore, its absorption can be extended towards the visible region, by reducing the band gap through doping with plasmonic-metals Ag, Al, Au, and Cu. The computed results reveal that the absorption for all the plasmonic-metal doped SrTiO₃ is completely shifted towards the visible region, resulting in widely known red-shift phenomena. This high absorption in the visible region makes doped-SrTiO₃ a potential candidate for optoelectronic applications. The dielectric constant and refractive index of the pristine and doped structures are also calculated and it is found that the absorption trend closely follows the dielectric constant. Furthermore, the evaluation of photocatalytic properties is also explored in the doped structures. Plasmonic-metal doping improves photocatalytic performance for all the dopants except Al. The doping with plasmonic-metals Ag, Al, Au, and Cu improves the optical properties (visible light absorption) and photocatalytic properties of pristine SrTiO₃, which opens a new prospect for potential applications in the field of optoelectronics.