Biotin-dependent acetyl-CoA carboxylases catalyze the committed step in type II fatty acid biosynthesis, the main route for production of membrane phospholipids in bacteria, and are considered a key target for antibacterial drug discovery. Here we describe the first structure of AccA3, an essential component of the acetyl-CoA carboxylase system in Mycobacterium tuberculosis (MTb). The structure, sequence comparisons, and modeling of ligand-bound states reveal that the ATP cosubstrate-binding site shows distinct differences compared to other bacterial and eukaryotic biotin carboxylases, including all human homologs. This suggests the possibility to design MTb AccA3 subtype-specific inhibitors.