Pea (Pisum sativum L.) produces seeds rich in proteins but yield and quality remain unstable across years due to various stresses. Sulfur (S) deficiency and water stress are two abiotic stresses that interact in the current context of climate change and low-input practices, and recent studies suggest an important role for sulfate transport and metabolism in the plant response to water stress. To investigate the interplay between sulfur nutrition and the water stress response, sulfate-deprived pea plants were subjected to a 9-days period of water stress during the early reproductive phase. While water stress did not impact seed yield, sulfur deficiency alone or combined with water stress decreased it by 38% and 63% respectively. Analysis of seed protein composition by one-dimensional electrophoresis revealed differences in the accumulation of sulfur-rich (11S) and sulfur-poor (7S) globulins in response to individual or combined stresses. To decipher the strategy used by plants to regulate the 11S/7S ratio in mature seeds, carbon, nitrogen (N) and sulfur partitioning between the different plant compartments was studied. Next, to pinpoint the mechanisms by which seeds adjust their metabolism under multi-stress conditions, early developing seeds were collected at three time points during drought and subjected to quantitative proteomics (shotgun). A total of 3184 proteins were identified and quantified, and 97 proteins were differentially accumulated in response to these stresses allowing the identification of candidate proteins that could control seed development or detoxification mechanisms.