The Asian long-horned beetle (ALB), a Cerambycidae, is an urban tree pest native to East Asia accidentally introduced to other continents via solid wood packing material. It was first detected in Europe in 2001, and since then infestations have been found in ten European countries. Using a 485-bp-long fragment of the mitochondrial barcode gene (COI), we studied the genetic diversity and structure of ALB populations in both native and invaded ranges, with a specific focus on Europe. Three main haplotypes were found across the native and invaded distribution of ALB. The native area in Asia was the most diverse with 23 haplotypes, but a low genetic structure was observed. Our results revealed up to nine distinct haplotypes that was diverged by no more than six mutational steps in European populations collected from 2001 to 2016. Nevertheless, the genetic structure was characterized by one widespread dominant haplotype in Europe. The overall complex genetic structure observed in Europe suggested a convoluted invasion scenario. Indeed, invasion history may include several introduction events as well as secondary dispersal.