Self-compassion has recently gained widespread attention by both researchers and clinicians due to its consistent association with better mental health outcomes. Despite this, few studies have investigated the underlying mechanisms for this relationship. This thesis aimed to examine psychological flexibility as a mediator for the relationship between self-compassion and mental health. This was derived from recent theoretical and practical interest in the relationship between self-compassion and Acceptance and Commitment Therapy. It was hypothesised that both self-compassion and psychological flexibility would be associated with better mental health, self-compassion would be associated with greater psychological flexibility and there would be a mediating relationship. Based on a dual-factor model of mental health, outcome measures included both positive and negative dimensions. Participants (N = 305) completed an online survey containing measures of self-compassion, psychological flexibility, wellbeing, flourishing, subjective physical health, psychological distress and social desirability. Results found support for all hypothesised relationships. Psychological flexibility may be an important mechanism by which self-compassion produces beneficial outcomes for mental health. Strengths, limitations and directions for future research will be discussed.