Mental health and substance use disorders in pregnant and postpartum people (PPP) are common, and most will not receive adequate treatment. In addition, Black PPP experience higher rates of mental health conditions and are less likely to receive treatment compared with White PPP. Yet, our understanding of the experience of Black PPP with respect to these conditions is limited. The goal of this study was to better understand these experiences with respect to mental health, substance use, and barriers to treatment. Semi-structured interviews were completed with 68 Black PPP who were pregnant or had been pregnant in the last 24 months to gain an understanding of mental health and substance use screening and treatment during the peripartum and postpartum period. Interview data were analyzed with qualitative software, using a qualitative content analysis method, informed by grounded theory. Four main themes were identified: (1) personal beliefs and views about mental health and substance use, (2) family and community beliefs about mental health and substance use, (3) personal experience with mental health and substance use, and (4) comfort in talking to others about mental health and substance use. Subthemes evolved within each of the four themes. Black PPP indicated that maternal mental health and substance use disorders are common in the Black community, but negative stigma related to these conditions often prevents PPP from talking about these conditions or seeking support or treatment despite believing that support and treatment can be beneficial. Clinical practice initiatives within this population can focus on advanced training for providers to more clearly understand personal experiences and related stigma related to mental health and substance use disorders, with the goal of supporting Black PPP mental health needs.