Extracellular ATP (eATP) is an ancient 'danger signal' used by eukaryotes to detect cellular damage. In mice and humans, the release of eATP during inflammation or injury stimulates both innate immune activation and chronic pain through the purinergic receptor P2RX7. It is unclear, however, whether this pathway influences the generation of immunological memory, a hallmark of the adaptive immune system that constitutes the basis of vaccines and protective immunity against re-infection. Here we show that P2RX7 is required for the establishment, maintenance and functionality of long-lived central and tissue-resident memory CD8 T cell populations in mice. By contrast, P2RX7 is not required for the generation of short-lived effector CD8 T cells. Mechanistically, P2RX7 promotes mitochondrial homeostasis and metabolic function in differentiating memory CD8 T cells, at least in part by inducing AMP-activated protein kinase. Pharmacological inhibitors of P2RX7 provoked dysregulated metabolism and differentiation of activated mouse and human CD8 T cells in vitro, and transient P2RX7 blockade in vivo ameliorated neuropathic pain but also compromised production of CD8 memory T cells. These findings show that activation of P2RX7 by eATP provides a common currency that both alerts the nervous and immune system to tissue damage, and promotes the metabolic fitness and survival of the most durable and functionally relevant memory CD8 T cell populations.