The halictid bee genus Homalictus (Apoidea: Halictidae) is distributed broadly across southeast Asia, Indonesia, Australia, and the archipelagos of the Pacific. The group is well represented in the bee faunas of Australia and Papua New Guinea, but Homalictus is particularly important in the Pacific where it plays a keystone pollination role as the only endemic bee group in many islands. Understanding the origin and radiation of this genus is therefore important for understanding plant-bee co-evolution, not only in the Pacific but the greater Oceania region. Previous studies have suggested that Homalictus has an Australian origin, and then dispersed northwards, but this is yet to be phylogenetically examined. Here we combine DNA sequences from the mitochondrial COI gene from Homalictus species from Papua New Guinea, the Pacific, and Australia to infer the geographical and climatic origins of this group and subsequent dispersal events. Our results indicate a tropical origin for Homalictus in Australia, followed by multiple dispersals into the Pacific and subtropical, temperate, and arid Australia. A tropical origin for Homalictus not only indicates the likely dispersal corridors for the ancestor of the group but has important implications for understanding social evolution in halictid bees.