Fatigue is associated with numerous harmful physical and mental health outcomes. Despite the established relationship between sleep and fatigue, research examining sleep variability within a person (i.e. intraindividual variability; IIV) and fatigue is limited. In addition, the associations between child and parent sleep regarding parent fatigue have not been explicitly explored, which could be relevant for parents of autistic children with increased sleep disturbance likelihood. The current study used two weeks of objective sleep (actigraphy) and subjective fatigue data from 81 parents and their children to explore associations among child sleep IIV, parent sleep IIV, and parent average daily fatigue, including evaluating evidence for mediation. Sleep IIV was estimated using a validated Bayesian model. Linear regression analyses indicated that greater parent total sleep time IIV predicted significantly higher fatigue levels. Child sleep IIV was unrelated to parent sleep IIV and fatigue, unsupportive of hypothesized mediation. Similarly, post hoc analyses examining child sleep averages, parent total sleep time IIV, and average parent fatigue were insignificant. Findings cautiously support the uniqueness of total sleep time IIV within parental sleep's relationship with fatigue, independent of child sleep. Objective sleep IIV should continue to be examined in addition to average levels.