Monoclonal antibodies (mAbs) and remdesivir, a small-molecule antiviral, are promising monotherapies for many viruses, including members of the genera Marburgvirus and Ebolavirus (family Filoviridae), and more recently, SARS-CoV-2 . One of the major challenges of acute viral infections is the treatment of advanced disease . Thus, extending the window of therapeutic intervention is critical . Here, we explore the benefit of combination therapy with a mAb and remdesivir in a non-human primate model of Marburg virus (MARV) disease . While rhesus monkeys are protected against lethal infection when treatment with either a human mAb (MR186-YTE; 100 %), or remdesivir (80 %), is initiated 5 days post-inoculation (dpi) with MARV, no animals survive when either treatment is initiated alone beginning 6 dpi . However, by combining MR186-YTE with remdesivir beginning 6 dpi, significant protection (80 %) is achieved, thereby extending the therapeutic window . These results suggest value in exploring combination therapy in patients presenting with advanced filovirus disease.