Aims <p>Na⁺/K⁺ homeostasis in plant cells plays a vital role in salt stress adaptation. The halophyte <i>Halogeton glomeratus</i> exhibits exceptional salinity tolerance through ion balance regulation. This study aimed to identify and characterize <i>HgS3</i>, a salt-responsive gene from <i>H. glomeratus</i>, and investigate its role in Na⁺/K⁺ homeostasis and salt tolerance.</p> Methods <p>We isolated and identified <i>HgS3</i> from <i>H. glomeratus</i> and determined its subcellular localization. Functional characterization was performed in yeast to assess its role in K⁺ and Na⁺ transport. Transgenic <i>Arabidopsis thaliana</i> expressing <i>HgS3</i> were generated, and their ion uptake and salt tolerance were evaluated. Transcriptome analysis was conducted to identify regulatory mechanisms in transgenic plants.</p> Results <p>HgS3 localized to the endoplasmic reticulum and exhibited leaf-predominant expression. Yeast assays showed that <i>HgS3</i> mediates K⁺ uptake at high Na⁺ concentrations while promoting Na⁺ absorption. Transgenic Arabidopsis expressing <i>HgS3</i> displayed enhanced salt tolerance, with increased Na⁺ uptake and reduced K⁺ efflux in both leaves and roots. Transcriptome analysis revealed conserved regulatory patterns, including upregulation of metal transporters, potassium transporters, and channel proteins, which collectively enhance Na⁺ absorption, limit K⁺ loss, and improve ion homeostasis.</p> Conclusions <p><i>HgS3</i> plays a critical role in Na⁺/K⁺ homeostasis by modulating ion transport under salt stress. Its overexpression enhances salt tolerance by increasing Na⁺ uptake while minimizing K⁺ efflux, providing a potential genetic target for improving crop resilience to salinity.</p>