The energetic burden of continuously concentrating solutes against gradients along the tubule may render the kidney especially vulnerable to ischaemia. Acute kidney injury (AKI) affects 3% of all hospitalized patients(1,2). Here we show that the mitochondrial biogenesis regulator, PGC1 alpha(3,4), is a pivotal determinant of renal recovery from injury by regulating nicotinamide adenine dinucleotide (NAD) biosynthesis. Following renal ischaemia, PGC1 alpha(-/-) (also known as Ppargc1a(-/-)) mice develop local deficiency of the NAD precursor niacinamide (NAM, also known as nicotinamide), marked fat accumulation, and failure to reestablish normal function. Notably, exogenous NAM improves local NAD levels, fat accumulation, and renal function in post-ischaemic PGC1 alpha(-/-) mice. Inducible tubular transgenic mice (iNephPGC1 alpha) recapitulate the effects of NAM supplementation, including more local NAD and less fat accumulation with better renal function after ischaemia. PGC1 alpha coordinately upregulates the enzymes that synthesize NAD de novo from amino acids whereas PGC1 alpha deficiency or AKI attenuates the de novo pathway. NAM enhances NAD via the enzyme NAMPT and augments production of the fat breakdown product beta-hydroxybutyrate, leading to increased production of prostaglandin PGE(2) (ref. 5), a secreted autacoid that maintains renal function. NAM treatment reverses established ischaemic AKI and also prevented AKI in an unrelated toxic model. Inhibition of beta-hydroxybutyrate signalling or prostaglandin production similarly abolishes PGC1 alpha-dependent renoprotection. Given the importance of mitochondrial health in ageing and the function of metabolically active organs, the results implicate NAM and NAD as key effectors for achieving PGC1 alpha-dependent stress resistance.