Primary Sjögren's syndrome (pSS) is a chronic autoimmune disorder characterized by exocrine gland dysfunction. Vitamin D3 (VD3), known for its immunomodulatory properties, has been implicated in modulating severity and immune responses in pSS, although the precise mechanisms are yet to be thoroughly investigated. This narrative review consolidates current research regarding the role of VD3 in pSS, with emphasis on its relationship with disease activity and immune function. Studies consistently reveal that VD3 levels are lower in pSS patients, with a negative correlation between VD3 levels and the severity of glandular damage, particularly in the salivary and lacrimal glands. Additionally, VD3 levels have been significantly associated with immune function markers, including T cell subset distribution and immunoglobulin levels. Despite the evidence, further investigation is needed to elucidate the causal relationships and mechanistic pathways involved. Overall, the existing data underscore the potential role of VD3 in the immunopathogenesis of pSS and suggest it may serve as a potential biomarker and adjunctive therapeutic target in future disease management approaches.