Improving the delivery of nucleic acids to diverse tissue types in culture is important for translating genome editing for regenerative cell therapies. Herein, we examine the effect of transfection media additives, such as the sulfated glycosaminoglycan heparin, in dramatically increasing pDNA delivery efficiency and transgene expression in a wide variety of cell types. Polyplexes formed by combining pDNA and Tr4, a cationic glycopolymer containing repeated trehalose and pentaethylenetetramine groups, were treated with low concentrations of heparin prior to in vitro transfection with plasmid DNA. Polyplex formulations were found to be stable and form ternary complexes upon heparin addition according to dynamic light scattering and ethidium bromide dye exclusion assays. Heparin-coated polyplexes offer significant increases (approximately 4-fold) in GFP expression compared to polyplexes prepared with Tr4 only in primary fibroblasts, U87, and HepG2 cells. Heparin was also shown to increase GFP expression in a linear, dose-dependent manner. The heparin-treated Tr4 polyplexes exhibited more than 50% higher cellular internalization with HepG2 cells while showing minimal increases with U87 and primary fibroblasts. Pharmacological inhibition was used to further understand the endocytic pathways taken during transfection in the presence and absence of heparin. It was found that heparin-treated polyplexes are endocytosed primarily through macropinocytosis and clathrin-mediated pathways, while Tr4 polyplexes without heparin appear to be internalized primarily via caveolae. Heparin appears to also modify the nuclear localization behavior of Tr4 polyplexes, which likely contributes to increased efficiency and transgene expression.