In this study, we identify leucyl-tRNA synthetase (LARS) as a breast tumor suppressor. To identify the mechanism underlying LARS-mediated breast tumor suppression, we first conducted charged tRNA profiling to assess charged and total tRNA-Leu expression in cell lines with high and low LARS expression. Expression of select charged and total tRNA-Leu isoacceptors were reduced in cell lines with lower LARS expression. We then conducted RNA-Seq and translation profiling including ribosome profiling (Ribo-Seq), polysome profiling in LARS-depleted cell lines. To test our hypothesis in vivo, we also performed RNA-Seq of ribosome-associated RNAs in Lars depleted PyMT tumors within RiboTag mice. The analyses implicate LARS as a regulator of leucine-rich translation. Overall design: To identify changes in tRNA-Leu expression, charged tRNA profiling was conducted in LARS-high non-transformed mcf10a cells compared to LARS-low HCC1806 breast cancer cells using charged tRNA profiling. To identify the impact of LARS on protein translation, RNA-Seq, Ribo-Seq and Polysome profiling were conducted in LARS-depleted 4T07 breast cancer cells. To assess the effects of LARS on translation in vivo, RNA-Seq was conducted on ribosome-associated mRNAs isolated from RiboTag mice harboring PyMT tumors, with and without monoallelic LARS deletion in the mammary tumor compartment.