Cell proliferation is a metabolically demanding process1,2. It requires active reprogramming of cellular bioenergetic pathways towards glucose metabolism to support anabolic growth1,2. NF-κB/Rel transcription factors coordinate many of the signals that drive proliferation during immunity, inflammation and oncogenesis3, but whether NF-κB regulates the metabolic reprogramming required for cell division during these processes is unknown. Here, we report that NF-κB organizes energy metabolism networks by controlling the balance between the utilization of glycolysis and mitochondrial respiration. NF-κB inhibition causes cellular reprogramming to aerobic glycolysis under basal conditions and induces necrosis on glucose starvation. The metabolic reorganization that results from NF-κB inhibition overcomes the requirement for tumour suppressor mutation in oncogenic transformation and impairs metabolic adaptation in cancer in vivo. This NF-κB-dependent metabolic pathway involves stimulation of oxidative phosphorylation through upregulation of mitochondrial synthesis of cytochrome c oxidase 2 (SCO2; ref. 4). Our findings identify NF-κB as a physiological regulator of mitochondrial respiration and establish a role for NF-κB in metabolic adaptation in normal cells and cancer.