Circulating concentrations of low-density lipoprotein cholesterol (LDL-C) and triglyceride-rich lipoproteins are leading risk factors for atherosclerotic cardiovascular disease¹. Despite several approved lipid-lowering medications, most patients fail to achieve target lipid levels under the chronic care treatment model^2,3. Here, we describe a potential single-course treatment in which an infusion of guide RNA and mRNA encoding a CRISPR adenine base editor—encapsulated within a GalNAc–lipid nanoparticle—leads to durable, liver-selective inactivation of angiopoietin-like 3 (ANGPTL3), a known driver of increased LDL-C and triglyceride concentrations. Analyses in human liver cells in vitro confirmed that the base editor introduces a DNA base-pair change at the target ANGPTL3 locus with no detectable off-target editing at any of approximately 3000 candidate sites or treatment-related structural variants. Targeted ANGPTL3 inactivation in nonhuman primates was well-tolerated and led to a > 90% mean reduction in circulating ANGPTL3 protein, with durability confirmed out to 3 years following a single dose. In mouse and nonhuman primate models of hyperlipidemia, gene inactivation was associated with reductions of approximately 40 to 50% in LDL-C and 50 to 70% in triglycerides. These results provided the scientific foundation for initiation of an ongoing first-in-human clinical trial in patients with refractory hyperlipidemia syndromes.