Chronic forms of depression often share many features with personality dysfunction and can be difficult to treat using traditional psychotherapies. To help improve treatment outcomes, individualized psychotherapies based on the individual’s specific problems and preferences that target interpersonal issues and have a longer duration of treatment have been recommended. The current case study follows a man diagnosed with persistent depressive disorder (PDD) and mixed personality features over the course of treatment that used an individualized and phase-based approach. An individualized and extended form of cognitive behavioral therapy (CBT) that shared similarities with cognitive-behavioral analysis system of psychotherapy (CBASP) was implemented to address the potential influence of early adverse life events, dysfunctional ways of thinking about the self and others that leads to increased depressed mood, and the influence of interpersonal situations in and outside the therapeutic relationship. Therapy was conducted in three phases (1. Psychoeducation/introduction to CBT; 2. modified CBT for insomnia and behavioral activation; 3. cognitive restructuring) during 32 weekly sessions over a period of nearly 11 months. Standardized measures administered over the course of treatment indicated significant reductions in depressive symptoms and improvements in self-efficacy. Qualitative reports from the client indicated improved satisfaction and quality of life as well as improved quality of relationships.