The development of efficient electrocatalysts for the CO₂ reduction reaction (CO₂RR) is essential to mitigate global energy and environmental problems. Single-atom catalysts (SACs) have become an emerging frontier in the CO₂RR because of the high utilization of noble metals, but they suffer from poor selectivity toward high-order hydrocarbons. Herein, using density functional theory calculations, we predict that homonuclear double-atom and triple-atom catalysts supported by two-dimensional Mo₂CO₂ exhibit superior catalytic performance for the CO₂RR compared to their single-atom counterparts. We show that the multi-nuclear reaction centers on multi-atom catalysts boost the adsorption of key CO₂RR intermediates, such as *HCOO and *CH, enabling selective reduction toward the CH₄ product at ultralow overpotentials. Besides, C–C coupling can also be facilitated on multi-nuclear sites, which enables an efficient production of the C₂H₅OH product. This work lays a foundation for the future development of multi-atom catalysts for the CO₂RR.