Angelman syndrome is a devastating neurogenetic disorder for which there is currently no effective treatment. It is caused by mutations or epimutations affecting the expression or function of the maternally inherited allele of the ubiquitin-protein ligase E3A () gene. The paternal allele is imprinted in neurons of the central nervous system (CNS) by the antisense () transcript, which represents the distal end of the small nucleolar host gene 14 () transcription unit. Reactivating the expression of the paternal allele in the CNS has long been pursued as a therapeutic option for Angelman syndrome. Here, we described the development of an antisense oligonucleotide (ASO) therapy for Angelman syndrome that targets an evolutionarily conserved region demarcating the start of the transcript. We designed and chemically optimized gapmer ASOs targeting specific sequences at the start of the human transcript. We showed that ASOs targeting this region precisely and efficiently repress the transcription of , reactivating the expression of the paternal allele in neurotypical and Angelman syndrome induced pluripotent stem cell-derived neurons. We further showed that human-targeted ASOs administered to the CNS of cynomolgus macaques by lumbar intrathecal injection repress and reactivate the expression of the paternal allele throughout the CNS. These findings support the advancement of this investigational molecular therapy for Angelman syndrome into clinical development (ClinicalTrials.gov, NCT04259281).