Advances in prenatal imaging, molecular diagnostic tools, and genetic screening have unlocked the possibility to treat congenital diseases in utero prior to the onset of disease pathogenesis. mRNA-based therapeutics, including gene editing approaches, have great potential for this application. However, a key challenge to realizing the curative potential of in utero gene editing therapies is safe and effective delivery of mRNA-based gene editing cargos. In this body of work, we explore the use of ionizable lipid nanoparticles (LNPs) to mediate somatic cell gene editing in the fetus. In Chapter 1, we overview the current landscape of delivery technologies for in utero gene therapies, including viral and non-viral platforms. In Chapter 2, we engineer a novel LNP platform for base editing in the perinatal brain, demonstrating strong efficacy in a mouse model of congenital brain disease, a fetal non-human primate, and human pediatric brain tissue. In Chapter 3, we investigate optimal microfluidic and excipient parameters for delivery of gene editing cargos and discover novel formulations that enhance gene editing in vitro and in vivo in the liver. In Chapter 4, we establish a novel approach for gene editing of hematopoietic stem cells by one-time administration of a targeted LNP platform in utero. In Chapter 5, we provide concluding remarks on the encouraging prospects of LNPs for therapeutic in utero gene editing of congenital diseases.