Improving the knowledge of the relationship between structure and properties is fundamental in catalysis. Recently, researchers have developed a variety of well-controlled methods to synthesize atomically precise metal nanoclusters (NCs). NCs have shown high catalytic activity and unique selectivity in many catalytic reactions, which are related to their ultrasmall size, abundant unsaturated active sites, and unique electronic structure different from that of traditional nanoparticles (NPs). More importantly, because of their definite structure and monodispersity, they are used as model catalysts to reveal the correlation between catalyst performance and structure at the atomic scale. Therefore, this review aims to summarize the recent progress on NCs in catalysis and provide potential theoretical guidance for the rational design of high-performance catalysts. First a brief summary of the synthetic strategies and characterization methods of NCs is provided. Then the primary focus of this review-the model catalyst role of NCs in catalysis-is illustrated from theoretical and experimental perspectives, particularly in electrocatalysis, photocatalysis, photoelectric conversion, and catalysis of organic reactions. Finally, the main challenges and opportunities are examined for a deep understanding of the key catalytic steps with the goal of expanding the catalytic application range of NCs.