Friedreich ataxia is caused by mutations in the frataxin gene, leading to neurodegeneration and premature death from cardiac dysfunction. Loss of frataxin impacts mitochondrial complex 1 (MC1) activity, suggesting MC1 may be a potential biomarker of frataxin levels and function. Biomarkers evaluated by noninvasive techniques are needed to monitor disease progression and treatment effects in people with Friedreich ataxia. PET with [F]BCPP-EF, a ligand with high binding specificity for MC1, was used to measure cardiac and brain MC1 density in a mouse model of Friedreich ataxia and in healthy volunteers and participants with Friedreich ataxia. An imaging protocol was developed in humans that included a 70-min brain scan immediately after administration of [F]BCPP-EF followed by a 60-min cardiac scan 255 min after [F]BCPP-EF administration. Cardiac [F]BCPP-EF binding in participants with Friedreich ataxia was lower than that in healthy volunteers and in a mouse model of Friedreich ataxia versus wild-type mice (∼50% reduction in both). In the brain, no statistically significant difference in the [F]BCPP-EF binding was detected between participants with Friedreich ataxia and healthy volunteers. Correlation analyses showed that blood frataxin and cardiac [F]BCPP-EF levels decreased with increasing guanine-adenine-adenine expansion size ( = -0.82 and -0.78, respectively; both < 0.05) but not in the precentral gyrus ( = 0.63; < 0.05). MC1 density as measured using [F]BCPP-EF-based PET may be a viable biomarker of mitochondrial deficit and frataxin levels in people with Friedreich ataxia.