Notch and basic helix–loop–helix E2A pathways specify cell fate and regulate neoplastic transformation in a variety of cell types. Whereas Notch enhances tumorigenesis, E2A suppresses it. However, whether and how Notch and E2A interact functionally in an integrative mechanism for regulating neoplastic transformation remains to be understood. It has been shown that Notch3‐induced T‐cell leukaemia is abrogated by the inactivation of pTα/pre‐T‐cell antigen receptor (pre‐TCR). We report here that Notch3‐induced transcriptional activation of pTα/pre‐TCR is responsible for the downregulation of E2A DNA binding and transcriptional activity. Further, the E2A messenger RNA and protein levels remain unaltered but the E2A inhibitor Id1 expression is augmented in thymocytes and T lymphoma cells derived from Notch3 transgenic mice. The increase in Id1 expression is achieved by pre‐TCR‐induced extracellular‐signalling‐regulated kinase 1/2. These observations support a model in which the upregulation of pre‐TCR signalling seems to be the prerequi‐site for Notch3‐induced inhibition of E2A, thus leading to the development of lymphoma in Notch3 transgenic mice.