Abstract Phylogenetic studies of globally distributed taxa are crucial to estimate the mode and tempo of common intercontinental biogeographic processes. However, few of these studies have focused on invertebrates, mainly because their taxonomy and species richness generally are highly neglected. Here we performed a morphological and mtDNA sequence-based species delineation analysis for 111 specimens of the cosmopolitan, speciose parasitoid wasp genus Spathius (Braconidae) and assessed its phylogenetic relationships and historical biogeography adding two nuclear markers. Seventy-one species of Spathius were delimited. Neither the monophyly of Spathiini, Spathius, nor its species groups were recovered. Based on the relaxed molecular clock and ancestral area reconstruction analyses, the Oriental appears as the most plausible region of origin for Spathius, whereas various intercontinental dispersal events probably played an important role in its species diversification. At least three and two dispersal events from the Oriental to the Ethiopian and Australian regions, respectively, were estimated to occur during the late Oligocene to mid-Miocene, c. 25–15 Mya. Dispersal to the Palaearctic and Nearctic from the Ethiopian region probably occurred during the early Miocene, c. 20 Mya. Our results overall reflect that the worldwide distribution of Spathius was acquired early in the evolutionary history of the lineage.