Objectives The objectives of this study were to investigate the associations of dispositional mindfulness and its facets with diet quality in Dutch adults with type 1 diabetes and type 2 diabetes and to evaluate the potential mediating role of emotional distress in these associations. Methods This was a cross-sectional study using data from the Diabetes MILES-The Netherlands. In total, 296 adults with type 1 diabetes and 364 with type 2 diabetes completed questionnaires. We assessed dispositional mindfulness by the Five Facet Mindfulness Questionnaire-Short Form, including total mindfulness and five facets: observing, describing, acting with awareness, being non-judgmental, and being non-reactive, and diet quality by the Dutch Healthy Diet 2015-index. Linear regression models were used to estimate the association. Mediation effects of depressive symptoms, anxiety symptoms, and diabetes-related distress were evaluated using the PROCESS macro with bias-corrected bootstrapped confidence intervals. Results Higher scores on the total mindfulness (β = 0.14, p = 0.02) and the observing facet (β = 0.15, p = 0.01) were significantly associated with higher diet quality in people with type 1 diabetes only, after adjustment for demographic factors. These associations were not mediated by depressive symptoms, anxiety symptoms, or diabetes-related distress. In adults with type 1 diabetes (but not type 2), higher dispositional mindfulness levels were associated with more optimal diet quality. Conclusions Higher mindfulness in general and observing in particular were related to a healthier diet with higher quality in Dutch adults with type 1 diabetes. Further longitudinal studies are warranted to understand the temporal relationship between mindfulness and diet quality.