The protection of DNA replication forks under stress is essential for genome maintenance and cancer suppression. One mechanism of fork protection involves an elevation in intracellular Ca ([Ca]), which in turn activates CaMKK2 and AMPK to prevent uncontrolled fork processing by Exo1. How replication stress triggers [Ca] elevation is unclear. Here, we report a role of cytosolic self-DNA (cytosDNA) and the ion channel TRPV2 in [Ca] induction and fork protection. Replication stress leads to the generation of ssDNA and dsDNA species that, upon translocation into cytoplasm, trigger the activation of the sensor protein cGAS and the production of cGAMP. The subsequent binding of cGAMP to STING causes its dissociation from TRPV2, leading to TRPV2 derepression and Ca release from the ER, which in turn activates the downstream signaling cascade to prevent fork degradation. This Ca-dependent genome protection pathway is also activated in response to replication stress caused by oncogene activation.