Ex vivo gene editing in T cells and hematopoietic stem/progenitor cells (HSPCs) holds promise for treating diseases. Gene editing encompasses delivery of a programmable editor RNA or ribonucleoprotein, often achieved ex vivo by electroporation and, when aiming to homology-driven correction, of a DNA template often provided by viral vectors together with a nuclease editor. Whereas HSPCs activate robust p53-dependent DNA damage response (DDR) upon nuclease-based editing, the responses triggered in T cells remain poorly characterized. Here, we performed comprehensive multi-omics analyses and found that electroporation is the main culprit of cytotoxicity in T cells, causing death and cell cycle delay, perturbing metabolism and inducing inflammatory response. Nuclease RNA delivery by lipid nanoparticles (LNPs) nearly abolished cell death and ameliorated cell growth, improving tolerance to the procedure and yielding higher number of edited cells compared to electroporation. Transient transcriptomic changes upon LNP treatment were mostly caused by cellular loading with exogenous cholesterol, whose potentially detrimental impact could be overcome by limiting exposure. Notably, LNP-based HSPC editing dampened p53 pathway induction and supported higher clonogenic activity and similar or higher reconstitution by long-term repopulating HSPCs compared to electroporation, reaching comparable editing efficiencies. Overall, LNPs may allow efficient and harmless ex vivo gene editing in hematopoietic cells for treatment of human diseases.