Despite the ecological importance of mesopelagic zooplankton, very little is known about their global distribution in the midwater realm, and even less information is available on global trends in their diversity. This study is the first attempt to explore the distribution, diversity gradients, and total biomass of mesopelagic mesozooplankton and micronekton in the global ocean. This study created the first quantitative Mesopelagic Mesozooplankton and Micronekton Database, organizing and standardizing a broad spectrum of literature sources for effective data analysis. Analyzing 861 mesozooplankton species using a range of species distribution models, the study found that the highest species richness was observed in the North Atlantic region, the west coast of India, and the Mediterranean Sea. Factors such as water temperature, euphotic zone depth, salinity, and dissolved nitrate concentration were essential for explaining their distribution. The results of this study indicate that NPP and POC are important factors that influence the biomass of mesopelagic mesozooplankton. The global mesozooplankton population in the mesopelagic zone was estimated using estimates of particulate organic carbon (POC) and primary productivity (NPP). Linear models fitted to predict mesopelagic mesozooplankton biomass using NPP and POC data were able to explain a moderate-to-substantial proportion of variance. The distribution patterns of mesopelagic mesozooplankton biomass showed enhanced values in certain regions, such as the Northern Hemisphere, west coasts of continents, and equatorial and 50°S bands. Global mesopelagic mesozooplankton biomass was estimated to range between 0.20-0.91 PgC, depending on the method used. Overall, this study provides an estimate of mesopelagic mesozooplankton biomass using the classical definition of the mesopelagic zone, and an estimate that considers the variable depth of this layer. The findings indicated that POC was a more reliable indicator of mesozooplankton biomass than NPP, particularly in more northerly latitudes. The research also showed that low mesopelagic mesozooplankton biomass is linked to low POC levels and low range-size rarity and species diversity, but higher biomass values are more often found in areas with moderate rarity values and high species diversity, combined with high POC.