Marine net primary productivity (NPP) underpins ocean food webs, global fisheries, and the ocean’s role in the carbon cycle, yet its global magnitude and long-term evolution remain highly uncertain. Differences among existing satellite-based NPP products have complicated efforts to robustly quantify marine productivity and its sensitivity to climate variability and change. Here, we compile an expanded global database of field NPP measurements determined by carbon isotope incubation, increasing observational coverage by ~50% relative to existing compilations. We observe spatially varying agreement between satellite products and in situ observations, motivating the development of an observationally constrained model that integrates field measurements with environmental predictors. This model demonstrates improved predictive skill and yields revised global NPP estimate ~10–20% lower than conventional satellite products, providing an alternative constraint on global marine primary productivity. Reconstructions over the satellite era further reveal a pronounced hemispheric redistribution of NPP, characterized by increasing spatial heterogeneity in the Northern Hemisphere and progressive homogenization in the Southern Hemisphere. These findings refine both the magnitude and spatial structure of marine productivity and have implications for understanding the ocean carbon cycle under ongoing climate change.