Niemann-Pick type C2 (NPC2) disease is an ultra-rare lysosomal storage disorder caused by deficiency of NPC2, involved in the egress of unesterified cholesterol from the endo-lysosomal compartment. NPC2 deficiency leads to pathological accumulation of cholesterol in lysosomes. Patients develop a severe, progressive neurological disorder together with relatively mild peripheral pathology. Affected patients usually die during the first or second decade of life. Currently, there is no effective treatment for NPC2 patients, representing a highly unmet medical need. Therefore, an in vivo gene therapy based on a single intra-cerebrospinal fluid (intra-CSF) administration of adeno-associated vectors (AAV) may offer the possibility of lifetime treatment. Here, we first developed a new mouse model of NPC2 disease that recapitulated the main hallmarks of the severe clinical phenotype. Next, we evaluated the therapeutic benefit of an intra-CSF delivery of AAV-Npc2 vectors in Npc2^-/- mice. AAV-mediated gene transfer resulted in significant decrease of unesterified cholesterol storage and correction of lysosomal pathology in CNS, leading to increased myelination and reduction in neurodegeneration (Purkinje cells) and neuroinflammation. After AAV-Npc2 delivery, liver was also efficiently transduced, providing a long-lasting source of therapeutic protein that allowed to correct peripheral cholesterol storage and lysosomal pathology. Finally, AAV-Npc2 treatment also resulted in normalization of locomotor deficits, improved body weight and considerably prolonged survival. Taken together, our results demonstrated that intra-CSF administration of AAV-Npc2 vectors led to widespread correction of both CNS and peripheral pathology in NPC2 mouse model. Thus, this study lays the foundation for the clinical translation of AAV-Npc2-based gene therapy.