Triple-negative breast cancer (TNBC), a distinct subtype of breast cancer, is characterized by the concurrent absence of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) in tumor tissues. This molecular phenotype renders current endocrine and targeted therapies ineffective, underscoring the urgent need to explore novel therapeutic targets. This study focused on icariin (ICA), a bioactive flavonoid derived from the traditional Chinese herb Epimedium, and systematically elucidated its mechanism in suppressing TNBC progression on the basis of its unique antitumor pharmacological properties. In vitro cell models and an in vivo pulmonary metastasis mouse model revealed that ICA significantly inhibited the malignant biological behaviors of TNBC cells (proliferation, invasion, and metastasis). RNA sequencing revealed significant alterations in the expression of key molecules of the JAK-STAT signaling pathway. Mechanistic investigations demonstrated that ICA suppressed the phosphorylation and activation of the JAK2/STAT3 signaling axis by downregulating spindle apparatus coiled-coil protein 1 (SPDL1). These experimental data confirmed that modulation of the SPDL1/JAK2/STAT3 signaling pathway constitutes the molecular basis of the anti-TNBC effects of ICA. This study elucidated the anti-TNBC mechanism of ICA at the signal transduction level, providing an innovative theoretical foundation for the development of natural product-based targeted therapies.