Oncolytic human herpes simplex virus type 1 (HSV-1) shows promising treatment efficacy in late-stage clinical trials. The anticancer activity of oncolytic viruses relies on deregulated pathways in cancer cells, which make them permissive to oncolysis. To identify pathways that restrict HSV-1 KM100-mediated oncolysis, this study used a pooled genome-wide short hairpin RNA library and found that depletion of the splicing factor arginine-rich splicing factor 2 (SRSF2) leads to enhanced cytotoxicity of breast cancer cells by KM100. Serine/arginine-rich (SR) proteins are a family of RNA-binding phosphoproteins that control both constitutive and alternative pre-mRNA splicing. Further characterization showed that KM100 infection of HS578T cells under conditions of low SRSF2 leads to pronounced apoptosis without a corresponding increase in virus replication. As DNA topoisomerase I inhibitors can limit the phosphorylation of SRSF2, we combined a topoisomerase I inhibitor chemotherapeutic with KM100 and observed synergistic anticancer effect in vitro and prolonged survival of tumor-bearing mice in vivo.