Triple-negative breast cancer (TNBC) is a highly aggressive disease with invasive and metastasizing properties associated with a poor prognosis. The STAT3 signaling pathway has shown a pivotal role in cancer cell migration, invasion, metastasis and drug resistance of TNBC cells. IL-6 is a main upstream activator of the JAK2/STAT3 pathway. In the present study we examined the impact of the NO-donor glyceryl trinitrate (GTN) on the activation of the JAK2/STAT3 signaling pathway and subsequent migration, invasion and metastasis ability of TNBC cells through in vitro and in vivo experiments. We used a subtoxic dose of carboplatin and/or recombinant IL-6 to activate the JAK2/STAT3 signaling pathway and its functional outcomes. We found an inhibitory effect of GTN on the activation of the JAK2/STAT3 signaling, migration and invasion of TNBC cells. We discovered that GTN inhibits the activation of JAK2, the upstream activator of STAT3, and mediates the S-nitrosylation of JAK2. Finally, the effect of GTN (Nitronal) on lung metastasis was investigated to assess its antitumor activity in vivo.