LEA_2 proteins are intrinsically disordered proteins implicated in plant abiotic stress tolerance; however, their functional characterization under salt and osmotic stress, particularly regarding stress-inducible peripheral redistribution, remains limited. SiLEA_2-6, an LEA_2 protein from the extreme-cold-tolerant species Saussurea involucrata, was identified from a cold-stress cDNA library, but its role in salt and osmotic tolerance remains unknown. In the present study, transgenic Arabidopsis thaliana Col-0 lines constitutively overexpressing SiLEA_2-6–eGFP were generated. Overexpression significantly enhanced salt and osmotic tolerance across germination, vegetative, and reproductive stages, as evidenced by improved germination rates, root elongation, survival, and physiological performance. Physiological analyses revealed improved membrane integrity (REL and MDA accumulation), enhanced osmotic adjustment, and preserved chlorophyll content. Subcellularly, SiLEA_2-6–eGFP displayed diffuse cytoplasmic distribution with intracellular punctate structures under non-stress conditions; within 60 min of salt or osmotic stress, it showed pronounced peripheral association, notably at guard cells and stomatal-adjacent regions. These findings demonstrate that SiLEA_2-6 enhances salt and osmotic tolerance in Arabidopsis, with stress-inducible peripheral enrichment consistent with a potential membrane-associated protective function. This study adds to the growing evidence that LEA_2 proteins confer tolerance not only to cold/freezing but also to salt and osmotic stress.