During acute infections, a small population of effector CD8(+) T cells evades terminal differentiation and survives as long-lived memory T cells. We demonstrate that the transcriptional repressor Blimp-1 enhanced the formation of terminally differentiated CD8(+) T cells during lymphocytic choriomeningitis virus (LCMV) infection, and Blimp-1 deficiency promoted the acquisition of memory cell properties by effector cells. Blimp-1 expression was preferentially increased in terminally differentiated effector and "effector memory" (Tem) CD8(+) T cells, and gradually decayed after infection as central memory (Tcm) cells developed. Blimp-1-deficient effector CD8(+) T cells showed some reduction in effector molecule expression, but primarily developed into memory precursor cells that survived better and more rapidly acquired several Tcm cell attributes, including CD62L and IL-2 expression and enhanced proliferative responses. These results reveal a critical role for Blimp-1 in controlling terminal differentiation and suppressing memory cell developmental potential in effector CD8(+) T cells during viral infection.