Background and aims <p>Salt stress significantly hinders banana growth and yield, making it essential to develop eco-friendly methods for enhancing salt tolerance. The study aimed to evaluate the integrated use of the marine-derived bacterium <i>Bacillus tequilensis</i> Bt-RS and its fermentation broth as a biostimulant for alleviating salt stress in banana seedlings.</p> Methods <p>The plant-growth-promoting traits and salt tolerance of Bt-RS were characterized. The chemical composition of its fermentation broth was determined using non-targeted metabolomics. The broth was then applied to banana seedlings (<i>Musa</i> AAA Cavendish var. Brazil) subjected to salt stress (70, 100, and 200 mM NaCl). Plant growth, ion homeostasis, physiological parameters, and rhizosphere microbiome composition were analyzed.</p> Results <p>Application of Bt-RS fermentation broth significantly enhanced plant height (by 20.55–33.64%), biomass, and physiological performance under salt stress. It maintained ionic homeostasis by reducing Na⁺ accumulation and increasing the K⁺/Na⁺ ratio. Under 100 mM NaCl, root superoxide dismutase activity increased by 69.39%, while malondialdehyde content decreased in roots (54.53%) and leaves (32.77%). Total soluble sugars increased by 152.31% in roots and 36.11% in leaves. The broth enriched beneficial rhizosphere taxa (e.g., <i>Bacillus</i>, <i>Burkholderia</i>) and enhanced metabolic and stress-resistance functional potentials.</p> Conclusion <p>The fermentation broth of <i>B. tequilensis</i> Bt-RS mitigates salt stress in banana through integrated ion regulation, antioxidant system enhancement, and beneficial microbiome modulation. It represents a promising biostimulant for sustainable banana production in salt soils.</p> Graphical Abstract <p></p>