Individuals with chronic stress can improve their overall wellness by making lifestyle changes. We describe the design and evaluation of a computer-animated conversational agent that is used in conjunction with Integrative Medical Group Visits (IMGV) to help individuals with chronic pain and depression manage their stress. The agent coaches patients in between group visit sessions, reviewing how to manage stress using non-pharmaceutical techniques (e.g., mindfulness, meditation, yoga self-massage). We conducted a longitudinal clinical trial with 154 participants in which patients in the intervention group interacted with the conversational agent at home on a touch screen tablet to reinforce what they learned in group medical visits. Results from the trial indicate that the conversational agent, in conjunction with medical group visits, leads to significantly more positive stress management behaviors in patients compared to outcomes that arise in usual care, after 9 and 21 weeks.