Diffuse midline glioma (DMG) is the most aggressive primary brain tumor in children. All previous studies examining the role of systemic agents have failed to demonstrate a survival benefit; the only standard of care is radiation therapy (RT), which provides transient symptomatic relief and limited survival advantage. Successful implementation of radiosensitization strategies in DMG remains elusive. In this project, we identify Napabucasin, an NAD(P)H Quinone Dehydrogenase 1 (NQO1)-bioactivatable reactive oxygen species (ROS) inducer, as a potent radiosensitizer in DMG both in vitro and in vivo. We show Napabucasin-mediated ROS production and cytotoxicity are dependent on NQO1, and establish the novel safety, feasibility, and survival benefit of convection-enhanced drug delivery (CED) of Napabucasin to circumvent the blood-brain barrier (BBB) concurrent with RT in an orthotopic DMG mouse model. Using this multi-modality strategy, we identify a promising treatment paradigm in DMG that may also be utilized to develop novel therapeutic treatments for other brain tumors.