The transcription factor BHLHE40 is an emerging regulator of the immune system. Recent studies suggest that BHLHE40 regulates type 2 immunity, but this has not been demonstrated in vivo.We found that BHLHE40 is required in T cells for a protective TH2 cell response in mice infected with the helminth Heligmosomoides polygyrus bakeri. H. polygyrus elicited changes in gene and cytokine expression by lamina propria CD4+ T cells, many of which were BHLHE40 dependent, including production of the common b (CSF2RB) chain family cytokines GM-CSF and IL-5. In contrast to deficiency in GM-CSF or IL-5 alone, loss of both GM-CSF and IL-5 signaling impaired protection against H. polygyrus. Overall, we show that BHLHE40 regulates the TH2 cell transcriptional program during helminth infection to support normal expression of Csf2, Il5, and other genes required for protection and reveal unexpected redundancy of common b chain-dependent cytokines previously thought to possess substantially divergent functions.