AimNurses' health advocacy (HA) role requires them to speak up for patients, clients, and communities in relation to healthcare. Various studies report the importance of the HA role of the nurse in healthcare. However, nurses' performance in this role is not clear yet. The present study aims to identify and explain how nurses perform their HA role in underserved populations.DesignQualitative grounded theory by Strauss and Corbin.MethodsData were gathered from three regional hospitals in Ghana with 24 registered nurses and midwives as participants through purposive and theoretical sampling techniques. Face‐to‐face in‐depth semi‐structured interviews were conducted from August 2019 to February 2020. The data were analysed using Strauss and Corbin's method and Nvivo software. The reporting follows Consolidated Criteria for Reporting Qualitative Research guidelines.FindingsThe HA role performance theory emerged from data with role enquiry, role dimension, role context, role influence, role reforms and role performance as building blocks. Data analysis showed that the main concerns of the nurses during their daily practice were mediating, speaking up, and negotiating. Among others, the intervening conditions were clientele influence and interpersonal barriers, whereas the outcome was a balance between role reforms and role performance.ConclusionAlthough some nurses proactively initiated biopsychosocial assessment and performed the HA role, most of them relied on clients' requests to perform the role. Stakeholders should prioritise critical thinking during training and intensify mentoring programmes in the clinical areas.Relevance for Clinical PracticeThe present study explains the process by which nurses perform their roles as health advocates in their daily activities as nurses. The findings can be used to teach and guide clinical practice for the HA role in nursing and other health care fields. There was no patient or public contribution.