Objective: The collaborative care model is effective in delivering evidence-based psychosocial oncology care. Social workers comprise the largest proportion of psychosocial oncology providers in the United States. This study describes the process and perceptions of clinical oncology social workers at a large comprehensive cancer center who transitioned to practicing as care managers within collaborative care. Methods: We describe the process of engaging clinical oncology social workers as care managers as part of the implementation of collaborative care at the Seattle Cancer Care Alliance. We then present survey results from 2017 and 2020 of participating social workers' perceptions of the collaborative care model's advantages and disadvantages. Results: Since the implementation of collaborative care at our institution, key functions of the social worker as care manager were defined. The majority of social workers surveyed in 2017 and 2020 agreed that collaborative care led to improved clinical outcomes, timely access to care, and greater patient satisfaction. They also reported professional advantages: more interdisciplinary team integration, working at the top of their licensure, and improved job satisfaction. Challenges identified included missing important patient needs and creating extra work burden for social workers. Conclusions: Oncology social workers can be successfully deployed as care managers within a collaborative care model, thus leveraging existing clinical staff to address unmet psychosocial patient needs. This model is feasible and sustainable in a large academic cancer center, requires minimal additional resources, and is favorably viewed by participating social workers in terms of perceived benefits to patients and their own professional roles.