Soil salinity poses a significant threat to agriculture by disrupting essential physiological processes in crops such as Zea mays. To address this challenge, the synergistic effect of the combined application of pullulan, an exopolysaccharide produced by Aureobasidium pullulans ATCC 42023, and the microalga Chlorella vulgaris was investigated to evaluate its potential as a biostimulant strategy to mitigate salt stress in maize. Pullulan was produced in a stirred-tank bioreactor (STR) using glucose as a carbon source at concentrations of 60, 80, and 100 g/L. The highest yield was obtained at 100 g/L, reaching a productivity of 0.28 g/g of substrate. The polymer was recovered via ethanol precipitation and characterized using FTIR spectroscopy. In preliminary bioassays, maize seeds were primed with pullulan solutions at concentrations of 0, 2.5, 5.0, and 10.0 g/L. The 2.5 g/L treatment significantly enhanced coleoptile and root elongation, while higher concentrations exhibited inhibitory effects. A salinity threshold of 300 mM NaCl was established to simulate salt stress conditions. To optimize the biopriming conditions, a Central Composite Design (CCD) was implemented, evaluating pullulan concentration (0.17–5.83 g/L) and microalgal biomass loading (3.4–116.5 mg). The resulting empirical model was statistically significant (p < 0.001; R² = 0.9762), predicting that moderate levels of both biostimulants maximized seedling height. Conversely, excessive microalgae loading inhibited growth, likely due to reduced water availability at the seed surface. In conclusion, the combined application of pullulan and Chlorella vulgaris demonstrated a synergistic biostimulant effect under saline conditions, enhancing germination and early growth of Zea mays. This integrated biopriming approach offers a promising and sustainable strategy to alleviate salinity-induced stress in crop production systems.