Photocatalytic CO₂ reduction to CH₄ is a promising strategy to solve the greenhouse effect and energy shortage problems. However, its application has been restricted by its low efficiency and poor selectivity. Herein, atomically thin defective TiO₂ is modified with iron tetraphenylporphyrin (FeTPP) to reinforce the selectivity of CO₂ reduction. The synthesized Fe-TiO₂-x photocatalyst exhibits a CH₄ production rate of 20.48 μmol g⁻¹ h⁻¹ and a CH₄ selectivity of 56.1% under visible light irradiation. Oxygen vacancies (OVs) of defective TiO₂ contributed to visible light absorption and FeTPP dispersion. The presence of FeTPP enhances the adsorption of CO intermediates, promoting the CH₄ selectivity. The conduction band of Fe-TiO₂-x lowers, inhibiting the CO generation. During the photoconversion process, CO₂˙⁻ and COOH⁻ intermediate products were detected by in situ DRIFTS. The synergistic effect of OVs and FeTPP improves the efficiency and selectivity of CO₂ photoreduction to CH₄. This work offers a new insight towards designing a photocatalyst for photoreduction of CO₂ to CH₄.