<p>The massive discharge of nitrate (NO₃⁻) represents a major challenge to the sustainability of both human society and ecosystems. Electrochemical reduction of NO₃⁻ to NH₃ offers a “turning waste into treasure” solution, enabling the conversion of renewable electricity into chemical energy stored in NH₃. In recent years, atomically precise metal nanoclusters (NCs) have attracted extensive research interest. Their protein-like hierarchical structures, from the metal core to the protecting layers, allow for multi-level design and synthesis, which not only offers a good means to tailor cluster structure at the atomic level for effective NO₃⁻ reduction, but also affords a paradigm for correlating cluster structure and catalytic performance. In this review, we summarize recent advances in atomically precise synthesis and electrocatalytic applications of metal NCs in NO₃⁻ reduction reactions. We first outline plausible mechanisms for the electrocatalytic NO₃⁻ reduction reactions, and then discuss the application of NCs in NO₃⁻ reduction based on their hierarchical architecture. We decipher design and synthesis strategies for metal NCs from four perspectives: metal core size, heteroatom doping, ligand engineering, and support engineering. Regarding the electrocatalytic applications of metal NCs, we aim to reveal the fundamentals governing the catalytic activity and selectivity for conversion of NO₃⁻ to NH₃. The fundamental and methodological advances systemized in this review should add to the acceptance of metal NCs in the electrocatalytic reduction of NO₃⁻.</p>