New wave therapies such as Acceptance and Commitment Therapy aim to cultivate people's psychological flexibility in order for them to live a satisfying life. Psychological flexibility has also a role in promoting mental health, which may mediate the relationship with life satisfaction. The aim of this study was to determine whether mental health mediates the effect of psychological flexibility on life satisfaction. A convenience sample of 140 adults (32 males, M = 36.50 years, SD = 12.22; 107 females, M = 38.46 years, SD = 12.81; and a 45-year-old person of unknown gender) completed an online questionnaire assessing psychological flexibility, mental health and life satisfaction. Three of the four hypothesized components of psychological flexibility (experiential acceptance, cognitive alternatives and cognitive control) contributed to the latent construct of psychological flexibility, but cognitive defusion failed to contribute. Psychological flexibility had a direct, positive effect on life satisfaction and the hypothesis that mental health would mediate this relationship was supported. The results suggest that psychological flexibility is important for one's mental health and that both are integral to life satisfaction. The results also support a continued focus on third-wave therapies in cultivating psychological flexibility.