As the healthcare landscape rapidly evolves to include advanced drug delivery methods with better cellular targeting and more efficient delivery, polymeric nanocarriers have emerged to close translational gaps. Acting on the central dogma of molecular biology, mRNA and protein therapeutics can offer curative potential for various debilitating diseases. Considering these advancements, polymeric nanocarriers have been widely explored preclinically in delivering both proteins and mRNA for various disease therapies. This review introduces how the next generation of polymeric nanocarriers can be designed for protein therapeutics, including some advantages and disadvantages as well as specific design considerations for mRNA vs protein delivery. The evolution of these polymeric nanocarriers is then examined, and the current landscape and emerging trends are presented. Finally, we provide an outlook on the clinical translation of polymeric nanocarrier delivery of mRNA and proteins, including a future perspective for the field. Despite the preclinical promise of these delivery systems in both mRNA and protein constructs, clinical translation is underwhelming. Continued development of polymeric nanocarriers is underway and early clinical trials have provided a foothold into translation for this technology. A key challenge for polymeric nanomedicine is bridging the gap between promising preclinical data and successful clinical translation.