Previous studies have found an inverse relationship between mindfulness and problem gambling severity. This paper presents the findings from two studies of treatment seeking problem gamblers designed to explore the role of mindfulness in problem gambling. Treatment-seeking problem gamblers displayed significantly lower mindfulness scores than adult community members and university students. Mindfulness was significantly related to most indices of gambling, and psychological distress was an important mechanism in these relationships. Rumination, emotion dysregulation and thought suppression were also implicated as mediators in the inverse relationship between mindfulness and psychological distress. Taken together, the findings provide theoretical support for existing models of mindfulness which suggest that mindfulness operates by reducing psychological distress through these cognitive mechanisms. They also suggest that mindfulness training may be a new and innovative avenue for therapy to improve treatment effectiveness for problem gambling.