The first tiphiid wasp (Aculeata: Euaculeata: Vespoidea: Tiphiiformes) in Cretaceous amber is described and figured. Thanatotiphia nyx, new genus and species, is represented by a male entombed in mid-Cretaceous (latest Albian) amber from Myanmar. Thanatotiphia possesses remarkable apomorphies in wing venation, lacks key traits of modern subfamilies, and is thus classified in a new subfamily, Thanatotiphiinae. The fossil is further shown to be nested well within the family, indicating that major lineages of Tiphiidae diverged by the mid-Cretaceous. The new taxon is compared with modern tiphiid subfamilies and the sparse fossil history of the family briefly overviewed.