Cancer cells depend on glutamine to sustain their increased proliferation and manage oxidative stress, yet glutamine is often depleted at tumor sites owing to excessive cellular consumption and poor vascularization. We have previously reported that p53 protein, although a well-known tumor suppressor, can contribute to cancer cell survival and adaptation to low-glutamine conditions. However, the TP53 gene is frequently mutated in tumors, and the role of mutant p53 (mutp53) in response to metabolic stress remains unclear. Here, we demonstrate that tumor-associated mutp53 promotes cancer cell survival upon glutamine deprivation both in vitro and in vivo. Interestingly, cancer cells expressing mutp53 proteins are more resistant to glutamine deprivation than cells with wild-type p53. Depletion of endogenous mutp53 protein in human lymphoma cells leads to cell sensitivity to glutamine withdrawal, whereas expression of mutp53 in p53 null cells results in resistance to glutamine deprivation. Furthermore, we found that mutp53 proteins hyper-transactivate p53-target gene CDKN1A upon glutamine deprivation, thus triggering cell cycle arrest and promoting cell survival. Together, our results reveal an unidentified mechanism by which mutp53 confers oncogenic functions by promoting cancer cell adaptation to metabolic stress.