Significance Epstein–Barr virus (EBV) is a human herpesvirus linked to the development of several cancers. We demonstrate that XPB, a component of the TFIIH transcription factor complex, is required for EBV lytic gene expression and virus production. We show that EBV SM protein regulates lytic gene transcription by utilizing XPB as a cofactor to activate specific target genes. Spironolactone blocks transcriptional activation by SM and spironolactone’s antiviral activity against EBV is mediated by degrading XPB protein. XPB is thus particularly important for expression of an SM-dependent group of EBV genes. Because SPR destabilizes XPB protein, inhibiting SM transcription function without affecting cellular gene-transcription machinery, XPB may be a useful therapeutic target to control EBV and other human herpesviruses.