Objectives To evaluate and describe the anti-herpesvirus effect of ASP2151, amenamevir, a novel non-nucleoside oxadiazolylphenyl-containing herpesvirus helicase–primase complex inhibitor. Methods The inhibitory effect of ASP2151 on enzymatic activities associated with a recombinant HSV-1 helicase–primase complex was assessed. To investigate the effect on viral DNA replication, we analysed viral DNA in cells infected with herpesviruses herpes simplex virus (HSV), varicella–zoster virus (VZV) and human cytomegalovirus. Sequencing analyses were conducted on an ASP2151-resistant VZV mutant. In vitro and in vivo antiviral activities were evaluated using a plaque reduction assay and an HSV-1-infected zosteriform-spread model in mice. Results ASP2151 inhibited the single-stranded DNA-dependent ATPase, helicase and primase activities associated with the HSV-1 helicase–primase complex. Antiviral assays revealed that ASP2151, unlike other known HSV helicase–primase inhibitors, exerts equipotent activity against VZV, HSV-1 and HSV-2 through prevention of viral DNA replication. Further, the anti-VZV activity of ASP2151 (EC50, 0.038–0.10 µM) was more potent against all strains tested than that of aciclovir (EC50, 1.3–27 µM). ASP2151 was also active against aciclovir-resistant VZV. Amino acid substitutions were found in helicase and primase subunits of ASP2151-resistant VZV. In a mouse zosteriform-spread model, ASP2151 was orally active and inhibited disease progression more potently than valaciclovir. Conclusions ASP2151 is a novel herpes helicase–primase inhibitor that warrants further investigation for the potential treatment of both VZV and HSV infections.