Duchenne muscular dystrophy (DMD) is a fatal, X-linked muscle disease caused by mutations in the dystrophin gene. Adeno-associated viral (AAV) vector-mediated gene replacement strategies hold promise as a treatment. Studies in animal models and human trials suggested that immune responses to AAV capsid proteins and transgene products prevented efficient gene therapy. In this study, we used widespread intramuscular (i.m.) injection to deliver AAV6-canine micro-dystrophin (c-µdys) throughout a group of skeletal muscles in dystrophic dogs given a brief course of commonly used immunosuppressants. Robust c-µdys expression was obtained for at least two years and was associated with molecular reconstitution of the dystrophin-glycoprotein complex (DGC) at the muscle membrane. Importantly, c-µdys expression was maintained for at least 18 months after discontinuing immunosuppression. The results obtained in a relevant preclinical model of DMD demonstrate feasibility of widespread AAV-mediated muscle transduction and transgene expression in the presence of transient immunosuppression to achieve molecular reconstitution that can be directly translated to human trials.