Group A Streptococcus (GAS, Streptococcus pyogenes) isolates of the recently described M1UK variant have emerged to cause human infections in the United States, several European countries, and elsewhere worldwide. Whole genome sequence analysis of M1 GAS isolates recovered from patients with invasive infections in many different countries in 2022 and 2023 discovered a close genomic relationship between some isolates from Scotland and most isolates from Iceland. The new M1UK subvariant was designated as M1GLC to reflect the historical relationship between the Gaelic populations in Scotland and Iceland. To expand this line of investigation, the genomes of 183 Scotland pharyngitis isolates recovered in 2022 and 19 Iceland asymptomatic carrier isolates recovered in 2023 were sequenced using Illumina short reads and Oxford Nanopore Technology long reads. Phylogenomic analysis demonstrated that all Iceland carrier isolates were very closely related and belonged to the M1GLC lineage. In contrast, the Scotland pharyngitis isolates were genomically diverse and belonged to the M1Global, M1UK, and M1GLC lineages. Sequence analysis of the sicgene encoding the Streptococcal Inhibitor of Complement, the most highly polymorphic gene in M1 GAS, identified more than 30 distinct alleles and confirmed that all M1GLC isolates are related by recent descent.The population genomic data are consistent with transmission of a single M1UK strain from Scotland to Iceland, where it rapidly spread to cause nearly all M1GLC GAS invasive infections and asymptomatic carriages in recent years.