The fourth most frequent disease in women is endometrial cancer (EC). The therapy choices for advanced-stage EC have limited options for treatment with a poor prognosis. In EC, there is an unmet need for identifying actionable drivers for the development of tailored therapies. Leukemia inhibitory factor receptor (LIFR) and its ligand LIF played important roles in cancer development, metastasis, stemness, and therapy resistance. However, little is known regarding the LIF/LIFR axis’s functional importance in EC development. Using endometrial tumor tissue arrays, researchers discovered that the expression of LIF and LIFR is increased in EC. The use of CRISPR/Cas9 to knock out LIFR in two distinct EC cells resulted in a substantial reduction in cell viability and survival. LIFR-KO dramatically decreased EC xenograft tumor development in vivo, according to in vivo studies. The treatment of established and primary patient-derived EC cells with EC359, a new LIFR inhibitor, resulted in cell viability decrease with an IC50 in the region of 20–100 nM and activation of apoptosis. Furthermore, EC359 therapy decreased EC cancer stem cell spheroid formation as well as the levels of cancer stem cell markers SOX2, OCT4, NANOG, and Axin2. Mechanistic investigations revealed that EC359 administration reduced the activation of LIF-LIFR-driven pathways in EC cells, including STAT3 and AKT/mTOR signaling. Importantly, EC359 therapy inhibited the development of EC patient-derived explants, EC cell line-derived xenografts, and patient-derived xenografts in vivo. Findings show that the LIF/LIFR axis has oncogenic potential in EC and support the use of the LIFR inhibitor EC359 as a new targeted treatment for EC by inhibiting LIF/LIFR oncogenic signaling.