<p>Soil salinization poses a significant threat to agricultural productivity, particularly affecting forage legumes such as alfalfa. Here, we reported the isolation and functional characterization of a novel salt-tolerant fungal strain, <i>Trametes</i> NF1, from a saline-alkali wetland in Tianjin, China, and demonstrated its potential to enhance alfalfa (<i>Medicago sativa</i> L.) growth and salinity tolerance. The strain was identified as belonging to the genus <i>Trametes</i> (phylum Basidiomycota) based on internal transcribed spacer (ITS) gene sequencing. Seed germination and seedling assays revealed that NF1 culture significantly improved alfalfa growth traits, including germination rate, root and bud lengths, stem diameter, leaf number, and fresh weight, with coefficients of determination (<i>R</i>²) ranging from 0.28 to 0.61 (<i>p</i> &lt; 0.01, regression analyses). At a 5% culture concentration, seed germination increased by 34%, and fresh weight by 61%, compared to the control. Biochemical analyses further indicated that NF1 application enhanced peroxidase activity by 201% and soluble protein content by 76%, while reducing malondialdehyde, soluble sugar, proline levels, along with the activity of superoxide dismutase, ascorbate peroxidase, and catalase, suggesting modulations of the antioxidant defense system and osmotic regulation. This study presents the first report of a <i>Trametes</i> strain from saline-alkali soil that promotes alfalfa salt tolerance, providing a novel microbial resource for sustainable management of salinized agroecosystems.</p>