On a global scale, breast cancer (BC) is the most prevalent malignancy among women. Triple-negative breast cancer (TNBC) is a subtype with a poor prognosis and high recurrence, metastasis, and mortality rates. Numerous studies have shown that the TAGLN gene participates in tumorigenesis and tumor invasion. However, TAGLN function in TNBC remains unknown. In this study, we screened 201 TNBC differential genes, including 133 up-regulated and 68 down-regulated genes. Gene Set Enrichment Analysis (GSEA) results showed that these differential genes were mainly enriched in DNA metabolic, nucleic acid binding biological process and gene expression, Rho GTPase, RHOBTB3, and cell cycle signaling pathways. Western blot indicated that TAGLN expression is lower in breast tissue than in normal tissue. However, the GSE38959 database showed that TAGLN is highly expressed in TNBC cells compared with mammary duct cells, and the CancerSEA database indicated that TAGLN is positively correlated with EMT, invasion, angiogenesis, differentiation, apoptosis, metastasis, proliferation, and stemness. Functionally, TAGLN promoted TNBC cell proliferation, migration, invasion, and cell cycle progression in vitro and tumor cell growth in vivo. Further mechanistic studies demonstrated that TAGLN promoted TNBC cell growth by regulating the AKT/CDK2 pathway. In sum, TAGLN is highly expressed in TNBC and promotes cell proliferation, migration, and invasion in vitro and tumor cell growth in vivo.