‘Design with the user’ is a guiding principle for creating digital solutions to solve systemic developmental challenges. According to this principle, digital solutions are more likely to be effective if the intended users are involved in the design process, thereby rooting design thinking in a human-centric approach that seeks to understand their characteristics, needs and challenges. However, few examples exist for human-centred design (HCD) processes being successfully applied in low-and-middle-income countries to create digital health interventions that achieve both scale and sustainability. This paper describes the application of a five-stage HCD process to develop a suite of mobile solutions to improve reproductive, maternal, neonatal and child health in Bihar, India, and discusses lessons learnt. Two of the solutions were later adopted by the government and scaled to 10 million subscribers and more than 300 000 front-line health workers (FLHWs) in 13 states. The socio-ecological model, which considers the interplay between individual, interpersonal, organisational, community and public policy factors, provides a conceptual framework for understanding key learnings from the HCD process. At the organisational level, we found that demand generation was constrained by deficiencies in the public health system, while at the community level, gender norms were a barrier to changing health practices. At the interpersonal level, mobile health solutions for mothers also had to address fathers, because they controlled women’s access to mobile phones. At the individual level, FLHWs had limited time to build their skills and needed more flexible, home-based learning opportunities; most FLHWs had access to mobile phones, but devices were overwhelmingly basic and digital skills limited; voice technology was required to maximise reach among low literate women and an authoritative yet empathetic narrator was required to humanise the digital experience, lend credibility and create engagement.