Wellbeing-defined broadly as experiencing one's life as enjoyable and fulfilling-has been associated with lower risk for Alzheimer's disease and related dementias. The mechanisms underlying this association are largely unknown. However, prior research and theory suggest that wellbeing impacts health behaviors and biological systems that are relevant to cognitive and brain health. Several of these factors have also been identified by the 2020 Lancet Commission on Dementia Prevention, Intervention, and Care as modifiable dementia risk factors. In the current review, we summarize and evaluate the evidence for associations between wellbeing and each of the 12 Lancet Commission risk factors. We found relatively consistent evidence for associations between higher wellbeing and lower levels of most of the risk factors: physical inactivity, social isolation, smoking, depression, hypertension, diabetes, hearing loss, traumatic brain injury, and air pollution. By contrast, we found evidence for only modest associations between wellbeing and education and mixed evidence for associations of wellbeing with alcohol use and body weight. Although most of the reviewed evidence was observational, longitudinal and experimental evidence suggests that many of the observed associations are likely bidirectional. These findings suggest that modifiable dementia risk factors may be mediators (i.e., intermediate steps in the causal chain) and/or confounders (i.e., variables that impact both wellbeing and dementia, and thus could induce a spurious association) of the association between wellbeing and dementia. We conclude by discussing next steps to test mediation hypotheses and to account for potential confounding in the relation between wellbeing and dementia.