Humoral immunity is critical for the prevention and control of viral infections, yet the specific B cells and mechanisms regulating antiviral responses in humans remain poorly defined. The Th1-associated transcription factor T-bet coordinates intracellular pathogen immune responses, and recent murine studies identified a T-bet-expressing B cell subset that mediates humoral antiviral immunity, but an analogous cell population has not been identified in humans. In this study, we sought to investigate the role of T-bet-expressing B cells during human viral infections. We identified T-bet expression within the memory B cell compartment of healthy individuals and described a relationship between the transcription factor and IgG1 and IgG3, two antiviral antibody isotypes. The T-bet+ B cell population was comprised of two discrete subsets: T-bet low resting memory cells and a highly activated, transcriptionally distinct T-bet high subset displaying an atypical memory phenotype. The T-bet high cell population transiently expanded in blood following vaccination with yellow fever or vaccinia virus; however, these cells were induced and maintained at an elevated frequency by chronic HIV viremia and were associated with increased expression and secretion of IgG1 and IgG3. The HIV gp140-specific response was maintained almost entirely by T-bet+ memory B cells in both viremic and aviremic donors. Together, our findings identify T-bet is a critical regulator of humoral antiviral immunity in humans and suggest T-bet+ B cells specifically mediate the humoral immune responses to live viral vaccines and HIV.