Introduction: Depression and anxiety disorders affect individuals' everyday lives, and treatments that can help them to perform everyday occupations are needed. Occupational therapy for this group has been evaluated from a short-term perspective but not from a long-term perspective; further research is thus warranted. The aim of the study was to investigate the longitudinal outcomes of the Tree Theme Method (TTM) compared with care as usual, provided by occupational therapists, in terms of everyday occupations, psychological symptoms, and health-related aspects. Methods: This randomised controlled trial comprised a follow-up 3 and 12 months after an intervention. A total of 118 participants (19–64 years) with depression or anxiety disorders and problems with everyday occupations completed the base line questionnaires, 100 completed the follow-up at 3 months, and 84 completed the follow-up at 12 months. Imputations of missing data were performed using the last observation, and parametric analysis was used. Results: Both groups showed significant improvements (P value ≤ 0.01) in everyday occupations, psychological symptoms and health-related aspects after 3 and 12 months. No significant differences were found between the groups. Conclusion: This study contributes with knowledge about the outcomes of occupational therapy for clients living with depression and anxiety disorders. Both TTM and care as usual lead to significant improvements over time concerning everyday occupations, psychological symptoms, and health-related aspects. The fact that both occupational therapy methods were associated with improvements for clients with depression and anxiety supports client-centredness in enabling an occupational therapist to choose the method best suited for the individual.