The physical properties of functional oxides can be fine-tuned by an appropriate dopant in the A and B sites of the perovskite lattice structure. In this study, cobalt (Co) was used as a dopant to investigate its influence on the structural, electronic, and optical properties of BaSnO3 using density functional theory (DFT) within WIEN2K-code based on the generalized gradient approximation (GGA) and the modified Becke-Johnson exchange potential (mBJ). Calculations were performed for BaSn1-xCoxO3 oxide with x = 0, 12.5, 25, 37.5 and 50%. Analyses of the studied materials have revealed that the lattice parameter has linearly decreased from 4.171 Å (x = 0%) to 4.069 Å (x = 50%) upon increasing Co-doping concentration. Pure BaSnO3 has an indirect energy bandgap (R–Γ) of 2.6 eV, while the valence band maximum (VBM) and the conduction band minimum (CBM) were both located in the Γ point of the Brillouin zone implying a direct energy bandgap for the Co-doped BaSnO3. Additionally, the optical energy bandgap was reduced by 46% for x = 50%. Moreover, the absorption coefficient has increased from around 1 × 105 cm−1 (x = 0%) to a maximum of about 6 × 105 cm−1 in the UV band and 2.5 × 105 cm−1 at the beginning of the visible band upon Co-doping (x = 50%). The present study, therefore, shows that Co-doped BaSnO3 is a very interesting material for the performance enhancement of oxides dedicated to photovoltaic and optoelectronic