<p>Dual-atom (DA) catalysts have exhibited great potential in regulating the catalytic performance of CO₂ reduction. However, there still exist huge challenges in the precise construction of DAs on a support. Herein, the precise immobilization of M-DAs (M = Ru, Rh, Pt) onto the Zr-oxo cluster of a 2D porphyrinic metal-organic framework (2D-Ni-PCN-222) was reported through a dimetallic complex pre-coordination strategy. The resultant M-DAs/2D-Ni-PCN-222 was applied in CO₂ photoreduction with ammonia borane as the H* donor. Under visible light, the optimal catalyst Ru-DAs/2D-Ni-PCN-222 displayed a HCOO⁻ production rate up to 35.4 mmol g⁻¹ h⁻¹ with nearly 100% selectivity and 691 h⁻¹ turnover frequency. Kinetic isotope experiments demonstrated that the coupling rate between H* and CO₂ governed the production efficiency of HCOO⁻. <i>In situ</i> experiments and density functional calculations disclosed that Ru-DAs with highly delocalized <i>d</i> electrons could accept the photo-generated electrons from 2D-Ni-PCN-222 and then inject to inert CO₂ molecules. Further <i>ab initio</i> molecular dynamics simulations revealed that the adaptive shortening of Ru–O coordination bonds during CO₂ adsorption played an important role in facilitating the deeper activation and the formation of optimal <i>η</i>³–O,C,O adsorption mode of the CO₂ molecule.</p>