The paper describes the development of Dynamic Interpersonal Therapy for use with complex depression (DITCC), and a pilot study testing DITCC’s effectiveness. The pilot found large pre-post improvements in well-being and distress; moderate rates of reliable improvement and clinically significant change; and curvilinear declines in depression and anxiety. Treatment completers and near-completers (N= 19) showed a significant curvilinear decline in symptoms of depression (PHQ-9) and anxiety (GAD-7). The results provide preliminary evidence that DITCC can be used as an effective treatment approach for complex depression. However, further research is needed to test its effectiveness in different settings with a larger sample size, using appropriate comparison groups under controlled conditions to further elaborate the short-term and long-term effects.