Depression is the leading cause of disability worldwide, with significant racial and ethnic disparities in diagnosis and treatment. Although Black adults in the United States are disproportionately exposed to psychosocial stressors, only one in four Black adults who need mental healthcare receive it, partly due to mental health stigma. This dissertation investigates using a smartphone-based Embodied Conversational Agent (ECA) counselor to reduce mental health stigma in the community to support mental health care-seeking intentions. Given the importance of religion in the lives of many African Americans and pre-existing close social relationships, this work was centered in predominately Black and African American faith communities. My dissertation research is the culmination of four years of community-engaged work in predominantly Black churches in Boston.During initial formative work, I created unique co-design methodologies to facilitate participant design contributions as a mechanism for designing technical innovations that reflect community goals, priorities, and cultural values. During this phase, participants identified their communities' assets and their most pressing health concerns, contributed to early design concepts and modalities, and emphasized the importance of creating features that address multiple facets of well-being. This work culminated in a field deployment that evaluated an initial version of an ECA-based mHealth application intervening on physical, social, and spiritual well-being.Leveraging these findings from earlier phases of this research, I synthesized a set of guiding design principles for developing digital mental health promotion interventions for predominantly Black church communities. In conjunction with principles from stigma theory and counseling psychology, I developed and evaluated an ECA-facilitated depression and stigmareduction intervention in a 14-day field deployment with 12 church members. The primary aim of this work was to develop a smartphone-based ECA to promote mental health and build a culture of community support for those experiencing mental illness.Participants found the mental health and stigma-reduction intervention acceptable, providing a range of satisfaction ratings significantly above neutral. Qualitative findings revealed how the application facilitated shifts in attitudes toward mental health and illness, primed care-seeking behaviors, and was used to support members experiencing mental illness.iii Acknowledgements Dear reader, if I have learned one thing during this academic journey, it would be that research and dissertations are never done alone. Over the last five years, I have had the invaluable support of mentors, lab mates, family, friends and participants. I'm lucky to have such a large community of people who have rallied around me.First, this work was conducted alongside and in collaboration with a team of investigators, support staff, and other PhD students. This work could not have come to fruition without these folks, and I'm grateful for th...