This study showed, in line with self-determination theory, that glycemic control among patients with type 2 diabetes (n  = 2866) was strongly associated with perceived self-care competence, which in turn was associated with autonomous motivation and autonomy-supportive health-care climate. These associations remained after adjusting for the effect of important life-context factors. Autonomous motivation partially mediated the effect of health-care climate on perceived competence, which fully mediated the effect of autonomous motivation on glycemic control. The results of the study emphasize health-care personnel’s important role in supporting patients’ autonomous motivation and perceived self-care competence.