Implementation of strengths model case management is increasing internationally. However, few studies have focused on its implementation process, and none have specifically addressed the implementation experience of direct-service practitioners. This paper presents factors that facilitate and impede the successful implementation of the strengths model, with a specific focus on practitioners who deliver the intervention directly to service recipients. To address this objective, a qualitative study of seven mental health agencies that implemented the model was conducted, involving a combination of participant observations and qualitative semistructured interviews with case managers, team supervisors, and senior managers. Qualitative data were analyzed using open coding followed by axial coding. Finally, the findings were aligned with an adapted Consolidated Framework for Implementation Research. Implementation of the strengths model involved a significant change in practice for case management practitioners. The results confirm that at the beginning of implementation, the strengths model was perceived as complex and not always adaptable to on-the-ground realities. With time, and with support from management, ongoing training and supervision sessions, and reflection and discussion, practitioners regained feelings of competence and resistance to the model diminished. The use of the model's structured team-based supervision tools was fundamental to supporting the implementation process by enabling an interactive and concrete training approach. The more an approach leads to changes in daily practice and is perceived as complex, the more concrete support is needed during implementation. This article highlights the importance of attending to a practitioner's sense of personal effectiveness and competence in the adoption of new practices.