Despite the promise of immune checkpoint inhibition (ICI), therapeutic responses remain limited. This raises the possibility that standard of care treatments delivered in concert may compromise the tumor response. To address this, we employed tobacco-signature HNSCC murine models in which we mapped tumor-draining lymphatics and developed models for regional lymphablation with surgery or radiation. Remarkably, we found that lymphablation eliminates the tumor ICI response, significantly worsening overall survival and repolarizing the tumor- and peripheral- immune compartments. Mechanistically, within tumor-draining lymphatics, we observed an upregulation of cDC1 cells and IFN-I signaling and show that both are necessary for the ICI response and lost with lymphablation. Ultimately, we provide a mechanistic understanding of how standard oncologic therapies targeting regional lymphatics impact the tumor response to immune- oncology therapy in order to define rational, lymphatic-preserving treatment sequences that mobilize systemic antitumor immunity, achieve optimal tumor responses, control regional metastatic disease, and confer durable antitumor immunity.