A new method was reported for the high-yield synthesis of a mononuclear Re(I) complex, fac-[Re(phen-dione)(CO)₃Cl] (where phen-dione = 1,10-phenanthroline-5,6-dione). The photochemical activity of the Re(I) complex for the photoreduction of CO₂ to CO was investigated under different conditions. Density functional theory (DFT) calculations were used to evaluate the photocatalytic mechanism for the photoreduction of CO₂ to CO in the presence of the Re(I) complex as a photocatalyst through a detailed comparison of two potential pathways: (I) regeneration of the initial catalyst, and (II) formation of a solvent-coordinated Re(I) complex. Although the theoretical calculations reveal that the regeneration of the initial photocatalyst through the reassociation of the Re(I) cationic intermediate with Cl⁻ is more thermodynamically favorable than the formation of a solvent-coordinated Re(I) species, the present results show that both catalytic cycles with the inclusion of solvation effects are thermodynamically favorable.