The plant bug, Pachypeltis micranthus Mu et Liu (Hemiptera: Miridae), is a potential biological control agent for Mikania micrantha H.B.K. (Asteraceae; one of the most invasive weeds worldwide). To date, only a few studies have investigated plant bugs. Here, we performed a chromosome-level genome assembly of P. micranthus using MGISEQ-2000 short-read, Nanopore, PacBio long-read, and high-throughput chromosome conformation capture (Hi-C) techniques. The assembled genome was 712.72 Mb in size, with a contig N50 of 16.84 Mb. Using the Hi-C technique, 71 scaffolds were assembled into 15 chromosomes, accounting for 99.96%. We predicted 11,746 protein-coding genes in P. micranthus with 96.20% complete benchmarking universal single-copy orthologs. Phylogenomic analysis showed that P. micranthus and two other Miridae bugs (Apolygus lucorum and Nesidiocoris tenuis) diverged from the common ancestor approximately 200.01 million years ago. Chromosome synteny analysis between P. micranthus and A. lucorum indicated high-level synteny. Many gene families including chemosensory genes and digestive and detoxification enzyme genes—were significantly expanded in the P. micranthus genome. These expanded gene families may indicate the bug to adapt to the single host plant. This high-quality chromosome-level genome assembly provides an invaluable resource for further molecular and evolutionary research on mirid bugs and also provides a basis for further research on biological control mechanisms for M. micrantha.