An estimated one third of the world's population is infected with Mycobacterium tuberculosis (Mtb) and suppresses the pathogen's replication without eradicating it, thereby remaining at risk for developing active tuberculosis (TB). It is not clear how Mtb survives, potentially for decades, in a hostile host environment. Respiration of nitrate to nitrite could help Mtb to survive in hypoxic tissues, but was not thought to be significant at physiologic oxygen tensions, nor was the resultant nitrite considered consequential to Mtb's physiology. Here, we found that Mtb infecting human macrophages in vitro produces copious nitrite at physiologic oxygen tensions. The nitrite impacts Mtb in diverse ways, slowing its growth, reducing its consumption of ATP, regulating its survival following treatment with isoniazid and hydrogen peroxide, and remodeling its transcriptome in a manner distinct from that of nitric oxide. Thus, respiration of nitrate and adaptation to nitrite are likely to play a prominent role in Mtb's pathophysiology, whether or not the Mtb resides in hypoxic sites.