The Himalaya Mountains are a biodiversity hotspot, boasting one of the world’s richest insect biotas. However, the primary mechanisms driving such high mountain biodiversity remain unclear. To address this, we use Scymnus, the largest genus of ladybirds, to explore the biogeographic origin and spatiotemporal evolution of the eastern Himalayan insect fauna for understanding the biological response to orogenic movement. Combining mitochondrial genomes and two nuclear genes (18S and 28S), we reconstructed the first highly supported and dated backbone phylogeny of Scymnus. Our findings strongly support the monophyly of Scymnus and identify seven major lineages within the genus. However, the subgenus Scymnus, Orthoscymnus and Pullus were found to be polyphyletic. We conclude that most extant Himalayan species originated through in situ speciation, with the Himalayan Scymnus lineage originating during the late Eocene and undergoing rapid diversification in the early Miocene. This diversification was likely triggered by the rapid uplift of the Himalayas and aligns with the recently proposed stepwise hypothesis of Himalayan orogenesis. Our findings, combined with net diversification rate analysis, indicate that new niche opportunities created by mountain uplift govern the diversification of the genus Scymnus. Furthermore, we found that the significantly higher diversity of Scymnus in mountains regions is driven by a combination of ecological factors, primarily the intensification of the Asian monsoon during the Miocene, which further strengthened the diversification of Scymnus in Himalayas. Our study provides a framework for biogeographic and evolutionary studies in eastern Himalayan Mountains, contributing to the understanding of the mechanism underlying.