Background and purpose Constitutive activation of Nuclear factor kappa B (NF-κB) signaling pathway is closely implicated in triple-negative breast cancer (TNBC) growth, metastasis and tumor immune escape. Therefore, the anti-cancer effects of icariin, a natural inhibitor of NF-κB, towards breast cancer cells and the underlying mechanisms were investigated. Experimental approaches Effects of cytotoxicity, anti-proliferation, apoptotic induction, anti-migration and anti-invasion of icariin were evaluated in TNBC cells and tumor mouse model. The inhibitory effect of icariin on SIRT6/NF-κB/epithelial-mesenchymal transition (EMT) signaling pathway was investigated by western-blot and transcriptomic analysis. The regulatory effect of icariin on tumor immunosuppressive microenvironment was evaluated. Key results Icariin selectively inhibited proliferation and triggered apoptosis in TNBC cells in a concentration- and time-dependent manner, but exhibited little cytotoxicity in normal breast cells. Moreover, icariin induced cell apoptosis via a mitochondria-mediated pathway, as indicated by upregulated ratio of Bax/Bcl-2 and ROS induction. Importantly, icariin impaired activation of NF-κB/EMT pathway by upregulating expression of SIRT6, resulting in inhibition of migration and invasion of breast cancer cells. Additionally, oss-128167, an inhibitor of SIRT6, dramatically attenuated anti-migration and anti-invasion effects of icariin. Notably, icariin exhibited a significant tumor growth inhibition and anti-pulmonary metastasis effect in a tumor mouse model of MDA-MB-231 and 4T1 cells by regulating tumor immunosuppressive microenvironment. Conclusions and implications Icariin could effectively trigger apoptosis and inhibit migration of breast cancer cells via the SIRT6/NF-κB signaling pathway, suggesting that icariin might serve as a potential candidate drug for the treatment of breast cancer.