Background: In Nigeria, there is an estimated 1.9 million people living with HIV (PLHIV), 53% of whom utilize HIV care and services. With decreasing HIV-related deaths and increasing new infections, HIV with its associated comorbidities continue to be a key public health challenge in Nigeria. Untreated, comorbid mental disorders are a critical but potentially modifiable determinant of optimal HIV treatment outcomes. This study aimed to identify the challenges and opportunities related to integrating mental health care into existing HIV programs in Nigeria. Method: Attendees at the Nigeria Implementation Science Alliance (NISA)’s 2019 conference participated in nominal group technique (NGT) exercise informed by the “Exploration, Preparation, Implementation, and Sustainment (EPIS)” framework. The NGT process was conducted among the nominal groups in two major sessions of 30-minutes phases followed by a 30-minute plenary session. Data analysis proceeded in four steps: transcription, collation, theming and content analysis. Results: The two major theoretical themes from the study were – opportunities and challenges of integrating mental health treatment into HIV services. Three sub-themes emerged on opportunities: building on health care facilities for HIV services (screening, counseling, task-sharing monitoring and evaluation frameworks) , utilizing existing human resources or workforce in HIV programs (in-service training and including mental health in education curriculum) and the role of social and cultural structures (leveraging existing community, traditional and faith-based infrastructures). Four sub-themes emerged for challenges: double burden of stigma and the problems of early detection (HIV and mental health stigma, lack of awareness) , existing policy gaps and structural challenges (fragmented health system) , limited human resources for mental health care in Nigeria (knowledge gap and burnout) and dearth of data/evidence for planning and action (research gaps) . Conclusions: Potential for integrating treatments for mental disorders into HIV services exist in Nigeria. These include opportunities for clinicians’ training and capacity building as well as community partnerships. Multiple barriers and challenges such as stigma, policy and research gaps would need to be addressed to leverage these opportunities. Our findings serve as a useful guide for government agencies, policy makers and research organizations to address co-morbid mental disorders among PLHIV in Nigeria.