The SecA2 protein export system is critical for the virulence of Mycobacterium tuberculosis. However, the mechanism of this export pathway remains unclear. Using a screen for suppressors of a secA2 mutant, we identified a new player in the mycobacterial SecA2 pathway that we named “SatS” for SecA2 (two) Suppressor. In M. tuberculosis, SatS is required to export a subset of SecA2 substrates and for growth in macrophages. We further identify a role for SatS as a protein export chaperone. SatS exhibits multiple properties of a chaperone, including the ability to bind to and protect substrates from aggregation.