Nuclear factor kappa B (NF-κB) promotes cell survival in response to genotoxic stress by inducing the expression of anti-apoptotic proteins including Bcl-xL, which protects mitochondria from stress-induced mitochondrial outer membrane permeabilization (MOMP). Here we show that the multifunctional sorting protein Pacs-2 (phosphofurin acidic cluster sorting protein-2) is required for Bcl-xL induction following DNA damage in primary mouse thymocytes. Consequently, in response to DNA damage, Pacs-2(-/-) thymocytes exhibit a blunted induction of Bcl-xL, increased MOMP and accelerated apoptosis. Biochemical studies show that cytoplasmic PACS-2 promotes this DNA damage-induced anti-apoptotic pathway by interacting with ataxia telangiectasia mutated (ATM) to drive NF-κB activation and induction of Bcl-xL. However, Pacs-2 was not required for tumor necrosis factor-α-induced NF-κB activation, suggesting a role for PACS-2 selectively in NF-κB activation in response to DNA damage. These findings identify PACS-2 as an in vivo mediator of the ATM and NF-κB-dependent induction of Bcl-xL that promotes cell survival in response to DNA damage.