Background Breast cancer is the most prevalent malignancy among women, it is crucial to identify sensitive biomarkers for prognosis and treatment of breast cancer patients. Emerging research has demonstrated the involvement of long noncoding RNAs (lncRNAs) in the advancement of breast cancer. LINC00534 has recently emerged as a potential regulator in multiple malignancies, yet its clinical significance and molecular mechanisms in breast cancer remain poorly characterized. Objective The purpose of this study was to explore the function of LINC00534 and miR-139-5p in breast cancer progression, as well as the mechanisms that underpin its actions. Methods Tumor and normal tissues were collected from 80 breast cancer patients. qRT-PCR was performed to detect LINC00534 expression in tissues. Kaplan-Meier analysis was used to assess survival differences between groups and the correlation between LINC00534 expression and clinical outcomes. CCK-8 assay was used to evaluate cell proliferation to assess LINC00534's effect on tumor growth. To evaluate the impact of LINC00534 on tumor metastasis, transwell assay was used to detect the migration and invasion abilities of cells. Moreover, dual-luciferase assay was used to verify the relationship within the LINC00534/miR-139-5p/HMGB2 axis. Result LINC00534 was significantly upregulated in breast cancer tumor tissues and cell lines (p < 0.001). Higher LINC00534 expression correlated with poorer prognosis in breast cancer patients, including shorter survival and higher recurrence risk (Log-rank p = 0.014). Furthermore, LINC00534 promoted breast cancer cell proliferation, migration, and invasion (all p < 0.001) via its interaction with the miR-139-5p/HMGB2 axis. Conclusion LINC00534 may serve as a prognostic marker and the LINC00534/miR-139-5p/HMGB2 axis could be a therapeutic target for breast cancer.