Viruses are intracellular pathogens that hijack host cell machinery and resources to replicate. Rather than being constant, host physiology is rhythmic, undergoing circadian (∼24 h) oscillations in many virus-relevant pathways, but whether daily rhythms impact on viral replication is unknown. We find that the time of day of host infection regulates virus progression in live mice and individual cells. Furthermore, we demonstrate that herpes and influenza A virus infections are enhanced when host circadian rhythms are abolished by disrupting the key clock gene transcription factor Bmal1. Intracellular trafficking, biosynthetic processes, protein synthesis, and chromatin assembly all contribute to circadian regulation of virus infection. Moreover, herpesviruses differentially target components of the molecular circadian clockwork. Our work demonstrates that viruses exploit the clockwork for their own gain and that the clock represents a novel target for modulating viral replication that extends beyond any single family of these ubiquitous pathogens.