Understanding the extent of population genetic connectivity in highly mobile marine species is vital for delineating management units. However, obtaining samples for generating genetic data is challenging for species inhabiting inaccessible pelagic waters. As a result, management strategies do not always align with underlying population biology. Marine strandings provide an accessible and cost effective sample sources for research on elusive cetaceans and can be used collaboratively among stranding networks to generate ecosystem wide population genetic assessments. Here, we used samples collected from strandings and free-ranging individuals across the North Atlantic to investigate population structure, genetic diversity and individual relatedness in the Atlantic white sided dolphin (AWSD Lagenorhynchus acutus), a widely distributed marine predator. Information from mitochondrial DNA and Single Nucleotide Polymorphisms (SNPs) showed a complete lack of population differentiation across the species’ range, implying an unusual pattern of strong connectivity. No differences in genetic diversity among geographic regions and weak within group relatedness further support the existence of species wide panmixia in AWSD. This study emphasises the value of long term stranding collections for cetacean research and has important implications for AWSD conservation management.