We used mitochondrial DNA (mtDNA) control region (CR) sequences and genotypes from eight microsatellite DNA (msatDNA) loci to determine the genetic structure of the school shark (Galeorhinus galeus) in New Zealand, Australia and Chile. The estimates of mtDNA haplotype and nucleotide diversity were very similar in New Zealand (h = 0.735 ± 0.032, π = 0.001 ± 0.001) and Australia (h = 0.729 ± 0.027, π = 0.001 ± 0.001), but in Chile they were higher (h = 0.800 ± 0.089, π = 0.002 ± 0.001). The haplotype genealogy showed evidence of two distinct clades, New Zealand and Australia combined (clade 1), and Chile (clade 2). A power analysis suggested that sample sizes were large enough to detect any significant differences within clade 1. Neutrality test, mismatch distribution, and demographic reconstructions based on a coalescence approach, suggested that the Oceania population (clade 1) went through a period of population expansion, whereas the population size of the Chile population (clade 2) has been relatively stable over the last 20,000 years. Data from microsatellite loci also supported the separation of the Oceania and Chile populations. Principal component analysis suggested that there might also be a separation of groups within clade 1, which was not statistically significant (P = 0.434). The genetic data reported in this study supported the model of a single G. galeus stock in New Zealand and Australia. Our findings were consistent with previous tagging data that showed individual G. galeus migrate across the Tasman Sea between Australia and New Zealand, and at least some of these migration events result in successful reproduction.