The aim of this study was to investigate the role of ascorbic acid in improving the agronomic and biochemical traits of psyllium under water deficit stress conditions. The experiment was conducted in a greenhouse with four irrigation regimes (100%, 75%, 50%, and 25% field capacity) and four concentrations of ascorbic acid (0, 5, 10, and 20 mM) in a factorial design based on a randomize complete block design. Averaged across all ascorbic acid levels, water deficit stress significantly reduced agronomic traits while increasing the mucilage, total phenol, total flavonoid content, and antioxidant activity of the seeds. HPLC analysis indicated that the highest levels of gallic acid were observed under stress conditions at 75% field capacity with a concentration of 5 mM (91.467 mg/100 g of seed). Rutin was found under normal conditions with 10 mM ascorbic acid and at 75% field capacity with 20 mM ascorbic acid (49.50 and 48.49 mg/100 g of seed, respectively). Additionally, p-coumaric acid was highest at 75% field capacity with 0 mM ascorbic acid (8.47 mg/100 g of seed), while cinnamic acid was also highest at 75% field capacity with 0 mM ascorbic acid (3.30 mg/100 g of seed). The metabolites apigenin and kaempferol were not detected in the seeds. The increase in seed yield and quality of P. ovata L. resulting from the exogenous application of ascorbic acid under both water stress and non-stress conditions could be a promising strategy for enhancing drought tolerance and increasing the production of bioactive compounds in seeds.