Body appreciation is a central facet of positive body image that has been associated with stronger psychological well-being in the autistic population. While longitudinal evidence suggests a bidirectional relationship between body appreciation and well-being over time in neurotypical populations, existing research in autistic people is limited to cross-sectional study designs. For the first time, therefore, this study examines prospective associations between body appreciation and psychological well-being (operationalised here as self-esteem, life satisfaction, and flourishing, respectively) in 262 autistic adults (aged 19-73 years; M = 38.43) from the United Kingdom. Participants completed two online surveys containing study measures at baseline and at 3-month follow-up. Cross-lagged panel modelling revealed unidirectional and positive associations between body appreciation and subsequent self-esteem and flourishing, but not with life satisfaction. Higher body appreciation at baseline predicted increases in self-esteem and flourishing over time, whereas no reciprocal effects were observed, and no longitudinal associations emerged for life satisfaction. These findings highlight the possible protective role of body appreciation in autistic people, strengthening claims that body appreciation could serve as a viable target of intervention aimed at promoting psychological well-being in autistic populations.