Though anger is a common human emotion, the unfettered behavioral expression of anger is often costly, contributing to a range of functional impairments, poor quality of life, and both physical and mental health problems. The current case illustrates how a third-generation cognitive behavioral therapy, Acceptance and Commitment Therapy (ACT), may be effective in reducing suffering linked with problematic anger. The client (“Robert”), a treatment-naïve man of low socioeconomic status, presented to a university training clinic reporting problematic anger outbursts that interfered with his relationships at work and with his girlfriend. The therapist conceptualized Robert’s problematic anger through the ACT psychological flexibility model, wherein Robert’s anger appeared to function as experiential avoidance to distance him from underlying emotional hurt. The therapist used ACT over 27 sessions to reduce Robert’s psychological inflexibility while promoting more psychological flexibility. Early sessions highlighted the unworkability of Robert’s anger, whereas subsequent sessions focused on clarifying values, loosening cognitive fusion, facilitating present moment awareness, and cultivating mindful acceptance in the service of living a meaningful life. The therapist monitored treatment progress using quantitative measures and qualitative reports. Collectively, the client showed notable gains. The case study adds to the growing body of literature supporting ACT for problematic anger.