CD4⁺ T cells producing interleukin-10 (IL-10) and interferon-γ (IFN-γ) are reported in chronic infections. However, the signals that direct the development of IL-10-producing T helper 1 (Th1) cells are undefined. We showed that development of IL-10-producing Th1 cells required high T cell receptor (TCR) ligation, sustained ERK1 and ERK2 MAP kinases phosphorylation, and IL-12-induced STAT4 transcription factor activation. Repeated TCR triggering led to enhanced IL-10 production by Th1 cells, and continued IL-12 action and high-dose TCR signaling were required for the development and maintenance of IL-10-producing Th1 cells. Although Th1, Th2, and Th17 cells require the activation of distinct STATs for their differentiation, activation of ERK1 and ERK2 was a common requirement for production of IL-10 by all Th cell subsets. IL-10 expression also correlated with c-maf expression. Despite having distinct functions in protection against pathogens, all Th cells share the important task of controlling overexuberant immune responses by means of IL-10 production.