Long non-coding RNA (lncRNA) LINC00173 has been previously shown to promote chemoresistance and progression of small-cell lung cancer. Herein, we examine the clinical significance and biological function of LINC00173 in triple-negative breast cancer (TNBC). Quantitative PCR analysis was performed to determine the expression of LINC00173 in TNBC and adjacent breast tissues (n = 84). The associations of LINC00173 expression with cancer features and survival of TNBC patients were analyzed. The function of LINC00173 in TNBC cell proliferation, colony formation, and invasion was explored. TNBCs expressed increased levels of LINC00173 relative to normal breast tissues. TNBC patients with high tumoral LINC00173 levels had a lower recurrence-free survival and overall survival rate than those with low LINC00173 expression. Silencing of LINC00173 inhibited the proliferation, colony formation, and invasion of TNBC cells, whereas overexpression of LINC00173 exerted opposite effects. In vivo studies confirmed the reduction of tumor growth by LINC00173 depletion. Mechanistic investigation revealed that LINC00173 suppressed miR-490-3p to promote aggressive phenotype in TNBC cells. There was an inverse correlation between miR-490-3p and LINC00173 in TNBC (r = -0.2647, P =  0.0149). Altogether, LINC00173 functions as an oncogene in TNBC through antagonization of miR-490-3p. Upregulation of LINC00173 is associated with poor prognosis in TNBC. Targeting LINC00173 provides a potential therapeutic strategy for TNBC.