Background: As Internet and smartphone use expands in India, there is an opportunity to develop mobile health (mHealth) interventions for marginalized populations, including men who have sex with men (MSM) and hijras/transgender women, hesitant to access traditional healthcare systems. Objective: The purpose of this study was to determine if an mHealth intervention was acceptable to MSM and hijras living in Mumbai, and if so, what features would be used. Methods: Data from four focus groups with MSM and interviews with four hijras, ten healthcare providers, and eight mHealth developers were thematically analyzed. Results: Once the need for an mHealth intervention was confirmed, comments about features were organized into three themes: content, usability, and retention. Content subthemes included providing sex education for younger community members, providing information about STIs, and providing information and social support for persons living with HIV. Usability subthemes included presenting content using pictures; using videos to present stories of role models; using push notifications for testing, appointment, and medication reminders; using geo-location to link to just-in-time services; and using telemedicine to increase access to healthcare providers and community services. Five retention subthemes included keeping it fun, using gaming mechanics, developing content in regional languages, protecting confidentiality, and linking to social networking apps. Conclusion: These findings may help inform mHealth development in India.