I L-7 is integral to the generation and maintenance of CD8⁺ T cell memory, and insufficient IL-7 is believed to limit survival and the persistence of memory CD8⁺ T cells. Here, we show that during the mouse T cell response to lymphocytic choriomeningitis virus, IL-7 enhanced the number of memory CD8⁺ T cells when its administration was restricted to the contraction phase of the response. Likewise, IL-7 administration during the contraction phase of the mouse T cell response to vaccinia virus or a DNA vaccine potentiated antigen-specific CD8⁺ memory T cell proliferation and function. Qualitatively, CD8⁺ T cells from IL-7–treated mice exhibited superior recall responses and improved viral control. IL-7 treatment during the memory phase stimulated a marked increase in the number of memory CD8⁺ T cells, but the effects were transient. IL-7 therapy during contraction of the secondary CD8⁺ T cell response also expanded the pool of memory CD8⁺ T cells. Collectively, our studies show differential effects of IL-7 on memory CD8⁺ T cell homeostasis and underscore the importance of the timing of IL-7 therapy to effectively improve CD8⁺ T cell memory and protective immunity. These findings may have implications in the clinical use of IL-7 as an immunotherapeutic agent to bolster vaccine-induced CD8⁺ T cell memory.