The Old World buntings (Aves: Emberizidae) mainly inhabit open habitats in Eurasia and Africa. It has long been debated whether the group originated in the New World or the Old World and whether their radiation is related to the expansion of open habitats and shifts in migratory behaviours. To answer these questions, we reconstructed their biogeographic histories and analysed their diversification patterns in terms of time, space and traits using a near-complete phylogeny. We found the most recent common ancestor of Emberizidae and their sisters distributed in the New World. After invasion into the eastern Palearctic through the Bering Straits Bridge in the middle Miocene, subsequent loss of migrations probably split Emberizidae into two lineages: one radiated in Afrotropical deserts and savannah and the other mainly diversified in Palearctic semi-open to open forests. The mountains of Central Asia and the Qinghai-Tibetan Plateau's group began to diversify in the late Miocene (~10 Ma), at first rapidly, coinciding with the expansion of open habitats due to global cooling. As the available habitats were occupied, the diversification rate of buntings decreased rapidly in arid habitats, but shifts of habitat preference to open forests led to terminal radiations on the southern edge of taiga forests in the mountains of Central Asia and the eastern Palearctic. Our results provide insight into the biogeographic histories and radiation of the Old World buntings in open habitats.