Nicotinamide adenine dinucleotide (NAD+) can be synthesized by nicotinamide phosphoribosyltransferase (NAMPT). We aimed to determine the role of NAMPT for maintaining NAD+ levels, mitochondrial function, and metabolic homeostasis in skeletal muscle cells. We generated stable Nampt knockdown (shNampt KD) C2C12 cells using a shRNA lentiviral approach. Moreover, we applied gene electrotransfer to express cre recombinase in tibialis anterior muscle of floxed Nampt mice. In shNampt KD C2C12 myoblasts, Nampt and NAD+ levels were reduced by 70% and 50%, respectively, and maximal respiratory capacity was reduced by 25%. Moreover, anaerobic glycolytic flux increased by 55% and 2-deoxyglucose uptake increased by 25% in shNampt KD cells. Treatment with the NAD+ precursor nicotinamide riboside restored NAD+ levels in shNampt cells and increased maximal respiratory capacity by 18% and 32% in control and shNampt KD cells, respectively. Expression of cre recombinase in muscle of floxed Nampt mice reduced NAMPT and NAD+ levels by 38% and 43%, respectively. Glucose uptake increased by 40% and mitochondrial complex IV respiration was compromised by 20%. HIF1α-regulated genes and histone H3 lysine 9 (H3K9) acetylation, a known SIRT6 target, were increased in shNampt KD cells. Thus, we propose that the shift towards glycolytic metabolism observed, at least in part, is mediated by the SIRT6/HIF1α axis. Our findings suggest that NAMPT plays a key role for maintaining NAD+ levels in skeletal muscle and that NAMPT deficiency compromises oxidative phosphorylation capacity and alters energy homeostasis in this tissue.