Aims: To investigate a hypothesised process model based on self-determination theory (SDT) in a population of people with type 2 diabetes. The model suggests that autonomy support from healthcare professionals is an important determinant of autonomous motivation and perceived competence in diabetes, which correlate positively in turn with wellbeing and negatively with HbA1c. Methods: This cross-sectional study used baseline questionnaire data and HbA1c levels from a randomised controlled trial investigating the effects of a person-centred consultation program. The questionnaire used validated scales and items assessing autonomy support, wellbeing, motivation, self-care activities, diabetes distress and perceived competence. Pearson correlations were calculated, and mediation analysis was conducted by multivariate linear regression analysis. Results: 116 participants completed the questionnaire. Autonomy support was significantly correlated with perceived competence and controlled motivation. Perceived competence correlated negatively with diabetes distress and positively with self-care activities. Diabetes distress correlated negatively with wellbeing. Controlled motivation correlated positively with autonomous motivation, which correlated positively with both wellbeing and self-care activities. Self-care activities correlated negatively with HbA1c. Conclusion: As suggested by the hypothesised SDT process model, autonomy support, autonomous motivation and perceived competence are associated with better wellbeing and improved HbA1c.