Out-of-wedlock pregnancy among adolescents in sub-Saharan Africa is a major concern, because of its association with health, social, psychological, economic and demographic factors. This article describes the development of the Teenage Mothers Project, a community-based intervention to improve psychological and social well-being of unmarried teenage mothers in rural Uganda. We used Intervention Mapping (IM) for systematically developing a theory and evidence-based comprehensive health promotion programme. A planning group consisting of community leaders, teenage mothers, staff of a community-based organization and a health promotion professional was involved in the six steps of IM: needs assessment, programme objectives, methods and applications, intervention design, planning for adoption and implementation and planning for evaluation. The programme includes five intervention components: community awareness raising, teenage mother support groups, formal education and income generation, counselling, and advocacy. The intervention components are based on a variety of theoretical methods, including entertainment education, persuasive communication, mobilization of social networks and social action. In conclusion, IM facilitated the planning group to structure the iterative, bottom-up, participatory design of the project in a real-life setting and to use evidence and theory. The article provides suggestions for the planning of support interventions for unmarried teenage mothers.