Streptococcus pyogenes (Group A Streptococcus, GAS) is a human-restricted pathogen that causes a wide range of diseases from pharyngitis and scarlet fever to more severe, invasive infections including necrotising fasciitis and streptococcal toxic shock syndrome. A hypervirulent acapsular chimeric emm4 lineage (emm4^C) has emerged in the USA, characterised by a gene fusion event between the GAS M protein (emm) and an adjacent M-like protein (enn). Despite exhibiting an in vitro growth defect, emm4^C isolates are the dominant emm4 lineage in the USA. A screen of clinical isolates from patients with invasive GAS (iGAS) disease revealed the presence of both a canonical emm4 and chimeric emm4^C strain in Australia. Using genomic, phylogenetic and phenotypic analyses, it was determined that the Australian emm4^C strain possessed the lineage-defining mutations associated with the US emm4^C clone. The emm4^C isolate was found to carry superantigen genes speA, speC and ssa, which play an important role in immune cell disruption and severe disease progression. The Australian emm4^C strain displayed increased virulence in an invasive murine model compared to the canonical emm4 isolate. This study represents the first report of the presence of the hypervirulent chimeric emm4^C clone in Australia. Future work will aim to evaluate the immune response against canonical emm4 and emm4^C isolate to determine whether immune escape due to the fusion of the emm and enn genes played a role in the emergence of the chimeric emm4^C.