In Envigado, Colombia, the Secretariat of Health has implemented, since 2011, an interprofessional program involving nurses to support and train relatives to improve the quality of life of people with a loss of autonomy and their family caregivers. The objectives of this study are to assess the outcomes of this program and to explore the contextual elements and mechanisms that can explain these outcomes. This article presents the research protocol for a realist evaluation that will be carried out to gather the perspectives of various local stakeholders involved. Four outcomes on family caregivers will be measured quantitatively using self-administered questionnaires and numerical scales. Contextual elements and mechanisms will then be explored qualitatively through focus groups and individual interviews. An iterative analysis will enable the refinement of a program theory. The results will inform a program theory that underlies the outcomes of the family caregiver support and training program. Community stakeholders, family caregivers, people with a loss of autonomy and their relatives will be involved in data collection and/or in the validation of the program theory.