Breast cancer is the most common malignancy among women and the leading cause of cancer deaths, with complicated pathogenesis that is largely unknown. In this study, we identified a novel long non-coding RNA (lncRNA) as a critical driver of breast cancer tumorigenesis. RUNX1 intronic transcript 1 (RUNX1-IT1) was notably overexpressed in human breast cancer tissues, and knockdown of RUNX1-IT1 inhibited breast cancer cell viability and invasion, as well as tumor growth in orthotopic transplantation model. Further, RUNX1-IT1 repressed ferroptosis, a novel iron-dependent form of regulated cell death, via increasing glutathione peroxidase 4 (GPX4) expression. Specifically, RUNX1-IT1 directly bound to N6-methyladenosine m⁶A reader IGF2BP1 and promoted the formation of (insulin like growth factor 2 mRNA binding protein 1) IGF2BP1 liquid-liquid phase separation (LLPS) biomolecular condensates, resulting in more IGF2BP1 occupation on GPX4 mRNA, increasing GPX4 mRNA stability. Moreover, high RUNX1-IT1 was linked to poor prognosis, and a strong positive correlation between RUNX1-IT1 and GPX4 was observed in clinical breast cancer tissues. Taken together, our data reveal that RUNX1-IT1 promotes breast cancer carcinogenesis through blocking ferroptosis via elevating GPX4, targeting of the previously unappreciated regulatory axis of RUNX1-IT1/IGF2BP1/GPX4 may be a promising treatment for patient with breast cancer.