Research on Moringa oleifera L.‘s potential applications as a dietary supplement, medicinal herb and plant growth enhancer under biotic and abiotic stresses has increased recently. Our study aimed to investigate the phytochemical screening of Moringa leaf aqueous extract (MLAE) and to determine its antimicrobial activity against pathogenic bacteria and fungi. Additionally, it investigated how MLAE biopriming affected tomato seedlings exposed to varying salinity levels. When three different MLAE concentrations (100, 250, and 500 μL) were tested against pathogenic microorganisms, an inhibitory zone appeared around the extract, demonstrating that MLAE could inhibit the growth of Bacillus sp., B. cereus, Klebsiella sp., Pseudomonas sp., P. aeruginosa, Acinetobacter sp., Fusarium sp1, Fusarium sp2, F. oxysporum. Moreover, aiming to mimic the negative effects of salt stress (0, 10, 25, 50 and 100 mM NaCl) on tomato seedlings, tomato seeds were soaked for 12 h in 0.1 and 0.2% of MLAE stock solution in addition to water (water priming, WP) and control unsoaked seeds. The results displayed that both germination and seedling growth traits were adversely affected by different NaCl concentrations, while seed soaking with MLAE alleviated the adverse effects of this stress. Most specially, MLAE significantly promoted plumule and radicle growth of tomato seedlings by the increases in seedling fresh and dry weights (mg) (246 ± 6.51a and 13.2 ± 0.35a) as compared with NaCl-free treatment (160 ± 4.233ef and 8.7 ± 0.23 fg). MLAE and WP application, under different salt concentrations, reduced the malondialdehyde content while increasing the antioxidant and phosphatase activities. Particularly, 0.2% MLAE caused the highest increase in protein and proline levels (2.54 mg/g fwt and 0.761 μmols/g fwt), followed by 0.1% MLAE and WP. Hence, this study affirmed the potency of MLAE as an antimicrobial agent against some pathogens and as a mitigator of salt stress in tomato seedlings suggesting its dual role in plant protection and stress tolerance as an eco-friendly and cost-effective alternative for integrated crop management.