Efficient and precise delivery of mRNA is critical for advancing mRNA therapies beyond their current use as vaccines. One of the limitations of lipid nanoparticles (LNPs) used for mRNA delivery is their non-specific targeting. This limitation can be overcome by functionalizing LNPs with antibodies that direct mRNA to the specific cells where it is needed. To address this challenge, we present a straightforward method to generate receptor-targeted LNPs that improve protein expression by nearly an order of magnitude compared to current cutting-edge targeting techniques. We achieved this by modifying LNPs with a highly specific antibody-capturing nanobody that anchors antibodies onto LNPs in an optimal orientation. This approach eliminates the need for purification of excess antibodies and ensures the optimal presentation of the antibody binding site. We have demonstrated that this technique can be used to rapidly screen a range of antibodies for optimal specificity and expression efficiency. Using these actively-targeted LNPs, we successfully transfected specific cell populations (T cells or B cells) of primary human peripheral blood mononuclear cells (PBMCs) ex vivo, with minimal off-target expression. Furthermore, we demonstrated systemic in vivo targeting of T cells in the liver, spleen, lung, circulating blood, and lymph nodes, with minimal delivery to other immune cells, compared to control particles. Additionally, our antibody-capturing LNP system showed no obvious toxic effects, as assessed by cytokine release profiles and spleen/liver histopathology imaging. As the therapeutic applications for mRNA mature, precise delivery will be crucial in maximizing therapeutic effects and minimizing off-target effects. Our simple antibody capture system will enable rapid screening for optimal receptors to target. We anticipate that the methods outlined here will have broad applicability for the delivery of a wide range of therapeutic nucleic acids.