Urbanization is a driving force of global biodiversity changes, and species that successfully adapt to city environments can become pests with the assistance of human factors. Here we present the first genomic data of Plecia longiforceps, an invasive pest exhibiting intensive outbreaks in the Seoul Metropolitan Area of Korea. HiFi and Pore-C sequencing data were used to construct a highly continuous genome assembly with a total size of 707 Mb and 8 major pseudochromosomes. Gene annotation using transcriptome data and ab initio predictions revealed significant numbers of genes related to detoxification and heat tolerance. Comparison to the Bibio marci genome showed high levels of synteny with some regions of chromosomal rearrangement. Our data will serve as an essential resource for population and functional genomic studies on dispersal and outbreaks of P. longiforceps, and facilitate research on eco-evolutionary processes of dipterans in urbanizing habitats.