Human telomerase reverse transcriptase (hTERT) may have noncanonical functions in transcriptional regulation and metabolic reprogramming in cancer cells, but it is a challenging target. We thus developed small-molecule ligands targeting hTERT promoter G-quadruplex DNA structures (hTERT G4) to downregulate hTERT expression. Ligand showed high affinity toward hTERT G4 ( = 1.1 μM) and potent activity against triple-negative breast cancer cells (MDA-MB-231, IC = 1 μM). In cell-based assays, not only exerts markedly inhibitory activity on classical telomere functions including decreased telomerase activity, shortened telomere length, and cellular senescence but also induces DNA damage, acute cellular senescence, and apoptosis. This study reveals that hTERT G4-targeting ligand may cause mitochondrial dysfunction, disrupt iron metabolism and activate ferroptosis in cancer cells. The antitumor efficacy of was also evaluated in an MDA-MB-231 xenograft mouse model and approximately 78.7% tumor weight reduction was achieved. No observable toxicity against the major organs was observed.