Adult stem cells (SCs) are essential for tissue maintenance and regeneration yet are susceptible to SC senescence during aging. Here we demonstrate the importance of cellular NAD+ level and its impact on mitochondrial activity as a pivotal switch to modulate muscle stem cell (MuSC) senescence. Importantly, the induction of the mitochondrial unfolded protein response (UPRmt) and of prohibitin proteins, subsequent to increasing cellular NAD+ with the precursor nicotinamide riboside (NR), rejuvenates MuSCs in aged mice. NR also prevents MuSCs senescence in Mdx mice, a mouse model of muscular dystrophy. Extending these observations to other SC pools and on the organism as a whole, we demonstrate that NR delays neural stem cell (NSC) and melanocyte stem cell (McSC) senescence, while also increasing mouse lifespan. Strategies that conserve cellular NAD+ could therefore be utilized to reprogram dysfunctional SCs in aging and disease to improve lifespan in mammals