CRISPR-based adenine base editors (ABEs) enable precise A•T-to-G•C conversion without double-strand breaks but are constrained by the packaging limits of adeno-associated viruses (AAVs), often requiring split systems with reduced efficiency. Here, we demonstrate lipid nanoparticles (LNPs) as a non-viral platform for delivering full-length ABE mRNA. LNP-delivered full-length ABE mRNA outperformed split formats in human DMD iPSCs and enabled efficient in vivo editing in a DMD-associated teratoma model. UTR optimization further enhanced ABE8e expression, achieving over 90% correction of a pathogenic splice-site mutation in spinal muscular atrophy models. In addition, subretinal delivery of UTR-optimized full-length ABE mRNA/sgRNA LNPs enabled efficient editing of the Vegfa exon 1 splice site in the mouse retina. These results establish LNP-mediated delivery of full-length ABE mRNA as a robust strategy to overcome viral packaging constraints and enable efficient genome editing.