The T cell receptor (TCR) is required for positive selection and the subsequent transition from the CD4(+)CD8(+) double-positive (DP) to the CD4(+) or CD8(+) single-positive (SP) stage of alphabeta T cell development. The molecular mechanism that maintains DP fate prior to the acquisition of a functional TCR is not clear. We have shown here that the structurally and functionally related transcription factors HEB and E2A work together to maintain DP fate and to control the DP to SP transition. Simultaneous deletion of HEB and E2A in DP thymocytes was sufficient for DP to SP transition independent of TCR. Loss of HEB and E2A allowed DP cells to bypass the requirement for TCR-mediated positive selection, downregulate DP-associated genes, and upregulate SP-specific genes. These results identify HEB and E2A as the gatekeepers that maintain cells at the DP stage of development until a functional alphabetaTCR is produced.