Over the last two decades, the molecular and cellular mechanisms underlying T cell activation, expansion, differentiation and memory formation. These studies have revealed that the generating of protective memory T cells depends on a variety of factors but it guided by a relatively small number of transcriptional regulators that determine T cell fate choices. One of these transcription factors, inhibitor of DNA binding (Id)2, is central in modulating the decisions that drive T cells commit to a particular fate outcome but the molecular mechanism underpinning this regulation has not been unclear. Here we have identified how this transcription factor regulates the appropriate formation of effector and memory T cell programs and how loss of Id2 cripples the capacity to rapidly induce the effector arm of the immune response. Our findings reveal that the Id2/E2A axis orchestrates T cell differentiation through the induction or repression of downstream transcription factors essential for effector and memory T cell differentiation.