We investigate how occupation influences the relationship between temperature and mortality in Mexico. Using multiple decades of nationwide death records---which include information on occupation---linked to local weather data, we find that heat-related mortality risk varies sharply by occupation. Young adults in climate-exposed jobs, especially in agriculture, experience significantly higher death rates from warm and hot temperatures. A 15 to 24 year-old agricultural worker is over 10 times more likely to die from heat exposure than a peer in professional or managerial employment, underscoring the role of occupation in climate vulnerability. These findings show that the burden of extreme heat disproportionately falls on the working poor. Our results suggest that implementing occupational safety measures and targeted heat adaptation policies (such as mandatory rest breaks and early warnings for outdoor workers) are essential to protect vulnerable workers. Furthermore, ongoing economic shifts away from highly exposed sectors may reduce increases in heat-related mortality due to climate change.