The objective of this study was to examine associations between the mindful parenting style of parents of adolescents (aged 12–18) with type 1 diabetes mellitus (T1DM), and the glycaemic control and quality of life (QoL) of the adolescents. Chronic health conditions, such as T1DM, that require demanding treatment regimens, can negatively impact adolescents’ quality of life. Therefore, it is important to determine whether mindful parenting may have a positive impact in these adolescents. Age, sex and duration of T1DM were examined as potential moderators. Parents (N = 215) reported on their own mindful parenting style (IM-P-NL) and the adolescents’ glycaemic control. Parents and the adolescents with T1DM (N = 129) both reported on adolescents’ generic and diabetes-specific QoL (PedsQL™). The results showed that a more mindful parenting style was associated with more optimal hemoglobin A1c (HbA1c) values for boys. For girls, a more mindful parenting style was associated with not having been hospitalized for ketoacidosis. For both boys and girls, a more mindful parenting style was associated with better generic and diabetes-specific proxy-reported QoL. In conclusion, mindful parenting style may be a factor in helping adolescents manage their T1DM. Mindful parenting intervention studies for parents of adolescents with T1DM are needed to examine the effects on adolescents’ glycaemic control and their quality of life.