Abstract <p><i>Brassica juncea’s</i> seed germination and seedling growth are critical stages of plant development, particularly in the presence of environmental stresses. The present study investigates the effects of seed priming with selenium selenate (Se) and humic acid (HA) on seed germination, seedling growth, and the concentrations of sodium (Na⁺) and potassium (K⁺) of <i>Brassica juncea</i> seedlings subjected to salt stress. NaCl concentrations ranging from 0 to 200 mM significantly inhibited seed germination, reduced chlorophyll content, and decreased water content, while promoting the accumulation of Na⁺ and reducing K⁺ concentrations in the leaves of the plants. Selenium priming at concentrations of 0.5 and 1.0 mM significantly improved germination parameters, including germination percentage (GP), germination energy (GE), and germination rate index (GRI), under both control and salinity stress conditions. Selenium also promoted root and shoot lengths and weights, particularly at the 0.5 and 1.0 mM concentrations, and enhanced chlorophyll <i>a</i> and <i>b</i> content across various NaCl concentrations. Furthermore, selenium priming increased K⁺ accumulation and improved the K⁺/Na⁺ ratio in the leaves. The addition of 5% HA significantly improved seed germination and seedling development, achieving GP of 70%, GE of 56%, and a GRI of 51.6 in non-saline conditions. HA effectively reduced growth limitations caused by salinity, with a 5% HA concentration significantly enhancing both root and shoot lengths and weights. HA at concentrations of 5% facilitates K accumulation under low NaCl concentrations. Both Se and HA treatments improved the levels of photosynthetic pigments in conditions of salinity stress. The addition of Se and HA at specific concentrations enhances the germination and seedling growth of <i>Brassica juncea</i> under salinity stress.</p>