This study presents a method for efficiently delivering genome-editing proteins both in vitro and in vivo using cationic lipid transfection reagents. The approach enables the delivery of proteins fused to anionic domains or those that natively bind to anionic nucleic acids. The method was tested with Cre recombinase, TALE and Cas9-based transcriptional activators, and Cas9:sgRNA nuclease complexes. In vitro, the delivery of these proteins into cultured human cells in media containing 10% serum resulted in up to 80% genome modification with higher specificity compared to DNA transfection. In vivo, the method was effective in delivering these proteins to the mouse inner ear, achieving 90% Cre-mediated recombination and 20% Cas9-mediated genome modification in hair cells. The study highlights the potential of cationic lipid-mediated delivery for improving the efficiency and specificity of genome editing. The method allows for the delivery of proteins that are otherwise difficult to enter mammalian cells, such as those that are highly anionic. The approach was shown to be effective for a variety of proteins, including Cas9:sgRNA complexes, which can be delivered into mammalian cells with high efficiency and minimal toxicity. The study also demonstrates that the delivery of Cas9:sgRNA complexes can lead to efficient genome modification with high specificity, as evidenced by the reduced off-target modification compared to DNA transfection. The study further shows that the delivery of Cas9:sgRNA complexes can be effective in vivo, with the ability to modify specific genomic loci in the mouse inner ear. The results suggest that cationic lipid-mediated delivery of genome-editing proteins can serve as a powerful tool and a potential in vivo strategy for the treatment of genetic diseases. The method is highly efficient, producing modification rates similar to or exceeding those of established nucleic acid transfection methods in cell culture, and enabling up to 90% and 20% genome modification rates in the inner ear hair cell population of live mice. The study also demonstrates that the delivery of Cas9:sgRNA complexes can lead to efficient genome modification with high specificity, as evidenced by the reduced off-target modification compared to DNA transfection.This study presents a method for efficiently delivering genome-editing proteins both in vitro and in vivo using cationic lipid transfection reagents. The approach enables the delivery of proteins fused to anionic domains or those that natively bind to anionic nucleic acids. The method was tested with Cre recombinase, TALE and Cas9-based transcriptional activators, and Cas9:sgRNA nuclease complexes. In vitro, the delivery of these proteins into cultured human cells in media containing 10% serum resulted in up to 80% genome modification with higher specificity compared to DNA transfection. In vivo, the method was effective in delivering these proteins to the mouse inner ear, achieving 90% Cre-mediated recombination and 20% Cas9-mediated genome modification in hair cells. The study highlights the potential of cationic lipid-mediated delivery for improving the efficiency and specificity of genome editing. The method allows for the delivery of proteins that are otherwise difficult to enter mammalian cells, such as those that are highly anionic. The approach was shown to be effective for a variety of proteins, including Cas9:sgRNA complexes, which can be delivered into mammalian cells with high efficiency and minimal toxicity. The study also demonstrates that the delivery of Cas9:sgRNA complexes can lead to efficient genome modification with high specificity, as evidenced by the reduced off-target modification compared to DNA transfection. The study further shows that the delivery of Cas9:sgRNA complexes can be effective in vivo, with the ability to modify specific genomic loci in the mouse inner ear. The results suggest that cationic lipid-mediated delivery of genome-editing proteins can serve as a powerful tool and a potential in vivo strategy for the treatment of genetic diseases. The method is highly efficient, producing modification rates similar to or exceeding those of established nucleic acid transfection methods in cell culture, and enabling up to 90% and 20% genome modification rates in the inner ear hair cell population of live mice. The study also demonstrates that the delivery of Cas9:sgRNA complexes can lead to efficient genome modification with high specificity, as evidenced by the reduced off-target modification compared to DNA transfection.