Cowpea is a promising crop for future Food Security in Sub-Sahra Africa (SSA) due to its nutritional value and resilience to extreme weather conditions like high temperatures and severe drought. However, projected climate changes threaten its production in SSA by exacerbating these weather conditions. While efforts have been made to improve cowpea yields by increasing the above-ground biomass, little attention has been given to enhancing its photosynthetic efficiency, which directly impacts harvest index and yield. This study investigates how heatwaves during the vegetative and reproductive stages independently affect cowpea photosynthesis and biomass using two genotypes with varying tolerance to heat. Heatwaves significantly reduced cowpea net photosynthesis and the number of grains per plant, with greater impact during the reproductive stage although the impact on photosynthesis and grain number are not directly correlated. The impact of heat on net photosynthesis could be associated with limited biochemical capacity of cowpeas during heatwave. These findings will contribute to understanding the factors of cowpea photosynthesis that need more focus for improving its photosynthetic efficiency and resilience. These insights are crucial for developing strategies to sustain cowpea productivity amidst changing climate conditions in SSA.