Duchenne muscular dystrophy (DMD) is a genetic disorder associated with mutations in the dystrophin gene that leads to the expression of a non-functional dystrophin protein, resulting in progressive loss of muscle function, and eventual death in the second or third decade of life. Current treatments, such as gene therapies which express a synthetic, miniature dystrophin protein missing many essential dystrophin protein domains, have shown limited improvement to disease prognosis and have not met critical endpoints. Further, gene therapies have potentially limited durability, particularly in pediatric patients due to cell turnover, immunological responses, and epigenetic silencing. By contrast, a gene editing approach could allow for lifelong benefits of muscle retention and function. We have previously described an approach to restore native dystrophin function by utilizing two ARCUS nucleases, delivered using a single AAV, to excise exons 45-55 of the dystrophin gene, resulting in a natural form of the dystrophin protein (del45-55 dystrophin) that is functionally competent and found in asymptomatic Becker Muscular Dystrophy patients. Up to 60% of DMD patients contain pathogenic mutations in this region, potentially allowing for broad applicability of this therapeutic approach. Here, we demonstrate functional improvement using clinical candidate ARCUS nucleases, in a humanized DMD mouse model. Following AAV delivery, we observed del45-55 dystrophin in multiple tissue types including heart and skeletal muscle, with evidence of the del45-55 dystrophin transcript in PAX7+ cells, a marker for muscle satellite stem cells. The maximum force output (MFO), a key functional readout, was significantly improved after ARCUS treatment, reaching 89% of the MFO levels observed in non-diseased mice. We show significant resistance to eccentric injury, reaching a 66% improvement compared to diseased untreated mice. This in vivo efficacy study further supports the therapeutic potential of an ARCUS gene editing approach for the treatment of DMD and ongoing development in clinical trials.