Mindful parenting is associated with greater adjustment and fewer behavior problems in children and adolescents. However, the mechanisms by which mindful parenting functions to mitigate risk in adolescence are not well understood. This study investigated parent emotional expression as a potential mechanism in the relationship between low mindful parenting and adolescent risk behaviors. A sample of 157 12–14-year-old adolescents (49 % female) and their primary caregivers (99 % female) participated in an emotionally arousing conflict interaction. Parents reported on their mindful parenting practices, and parents’ emotion expressions during the conflict interaction were coded including negative emotion, positive emotion, and shared parent-youth positive emotion. Adolescent substance use and sex behaviors were assessed through self-report, interview, and physical toxicology screens. Results indicated that mindful parenting was associated with less parental negative emotion and greater shared positive emotion during the parent-adolescent conflict. Further, results revealed a significant indirect effect of mindful parenting on youth’s substance use through shared parent-adolescent positive emotion. Findings highlight the relevance of emotional functioning in the context of stressful parenting situations in mindful parenting.