Objectives Considering health literacy needs is a key component of health services responsiveness to diabetes self-management among vulnerable individuals. The purpose of this qualitative study was to provide a detailed analysis of the health literacy of people with type 2 diabetes in relation to their daily self-care practices. Design Nested qualitative study in the ERMIES randomised controlled trial testing a 2-year structured care in type 2 diabetes. First round of semidirected interviews at the beginning of the trial with thematic analysis of content. Second round at the completion with directed interviews guided by the first round’s themes together with Health Literacy Questionnaire. Settings Interviews conducted at home. Participants Forty-four (31 females/13 males, 30–79 years, glycated haemoglobin (HbA1c)≥7.5%) consecutive participants out of 100 recruited in the ERMIES trial from 4 diabetology outpatient settings (Reunion Island). Forty-two respondents to the second round interviews. Results Three poles structured into eight themes characterised practices in context: health knowledge, disease management, expertise and social support. The relationships of participants in each of the eight themes were differentiated, ranging from functional to interactive and critical. Treatment and follow-up were essentially functional, while diet and exercise remained more interactive. Social support and relationship to health professionals were important determinants of disease management. Conclusions Treatment management and disease monitoring remain primarily the job of health professionals, as opposed to diet, physical activity and social support being part of ordinary practice. Decision-making, as a shared social task, as well as resources for participation in health services, should be considered for relevant interventions in type 2 diabetes. Trial registration number NCT01425866 .