<p>Breast cancer is a prevalent and highly heterogeneous malignancy that continues to be a major global health concern. Voltage-gated sodium channels are primarily known for their role in neuronal excitability, but emerging evidence suggests their involvement in the pathogenesis of various cancers, including breast cancer. However, the effect of β-subunits on breast cancer cells is not yet studied. SCN3B, as a modulatory subunit, is of particular interest due to its less understood role in cancer biology. This research comprehensively investigates the clinical associations, diagnostic potential, and functional role of SCN3B in breast cancer, shedding light on its diverse implications from patient outcomes to molecular mechanisms. Our methods included clinical data analysis from The Cancer Genome Atlas (TCGA) breast cancer dataset, diagnostic analysis through ROC curves, differential gene expression analysis, SCN3B expression assessment in cell lines, overexpression experiments, and functional assays. Additionally, we constructed a protein–protein interaction network to explore potential mechanisms underlying SCN3B’s impact. The study revealed significant clinical associations between SCN3B expression and various parameters such as tumor stage, race, age, histological type, molecular subtype, and hormone receptor status. SCN3B demonstrated strong diagnostic potential with an AUC of 0.95. It influenced the expression of over 800 genes, primarily associated with cell migration and extracellular matrix interactions. SCN3B exhibited distinct expression patterns between normal and breast cancer cell lines and successfully overexpressed in various breast cancer cell lines. This overexpression inhibited cell migration and invasion. Our research emphasizes SCN3B’s clinical relevance, diagnostic potential, and influence on cell behavior in breast cancer, offering insights into its multifaceted role and therapeutic implications.</p> Graphical Abstract <p></p>