We present a genome assembly of Petasites hybridus (Butterbur; Streptophyta; Magnoliopsida; Asterales; Asteraceae). The assembly consists of two haplotypes with total lengths of 2 802.87 megabases and 2 756.82 megabases. Most of haplotype 1 (95.61%) is scaffolded into 30 chromosomal pseudomolecules. Haplotype 2 was assembled to scaffold level. The mitochondrial sequence has a length of 302.34 kilobases and the plastid genome assembly has a length of 150.22 kilobases. Gene annotation of this assembly on Ensembl identified 41 187 protein-coding genes. This assembly was generated as part of the Darwin Tree of Life project, which produces reference genomes for eukaryotic species found in Britain and Ireland.