Emerging evidence indicates that heat stress significantly affects human health, labor productivity, and labor supply, calling for its inclusion in climate impact assessments. Agricultural labor, particularly vulnerable due to high work intensity and outdoor conditions, has been largely overlooked in these assessments. Here, we apply the widely used Wet Bulb Globe Temperature (WBGT) to measure the strength of heat stress based on three key variables including temperature, relative humidity, and air pressure. Projections of future changes in these climate variables in the Representative Concentration Pathway (RCP) 6.0 are translated to changes in WBGT, which is further applied to labor-heat response functions to derive the corresponding labor productivity loss. We incorporate heat-induced labor productivity shocks into a global economic multisector dynamic model, the Global Change Analysis Model (GCAM), to assess the impact of heat-induced productivity shock on global and regional agriculture. To explore the sensitivity of outcomes, we construct scenarios with climate projections from two General Circulation Models (GCMs), projected crop yield responses from two Global Gridded Crop Models (GGCMs), and two labor-heat response functions. Our findings suggest that, across scenarios, global agricultural labor productivity could decline by 5% to 18% by the end of the century, with the most severe impacts in Africa, South Asia, and Southeast Asia. In response to labor productivity loss, global agricultural employment may increase by 20 million (4%) to 92 million (18%), meanwhile, the production of major crops (corn, rice, wheat, and soybean) could decrease by up to 2%, and their prices could rise by up to 4%. These results demonstrate that the impact of labor response to a changing climate on the global agricultural market is equally important to the widely emphasized crop response in the literature, underscoring that omitting heat-induced labor productivity shocks underestimates the overall climate impact on global agriculture.