Photosynthesis is the process fuelling plant vegetative growth and development. Plants also rely on maternal photosynthesis to deposit food reserves in seeds. Intriguingly, prior to seed maturation, Arabidopsis embryos are also photosynthetically active. How embryonic photosynthesis impacts future seedling and adult plant development is poorly understood. Furthermore, addressing this question genetically is challenging since mutations perturbing photosynthesis are expected to do so in both embryos and vegetative tissues. We isolated a temperature-sensitive mutation affecting CPN60α2, encoding a subunit of the chloroplast chaperonin complex CPN60. When exposed to cold, cpn60α2 mutants accumulate less chlorophyll, decreasing embryonic photosynthesis. Combining the use of cpn60α2 mutants with independent genetic and pharmacological approaches, we show that embryonic photosynthetic activity is necessary for normal skoto- and photo-morphogenesis in juvenile seedlings as well as long-term adult plant development. Our results reveal the importance of embryonic photosynthesis activity for normal adult plant growth, development and health.