Background <p>Some populations remain chronically underserved to healthcare services because of poor housing conditions, lack of health insurance /administrative status, difficulties in French languages, disabilities, …. Health mediation, by promoting the ability of services to adapt their organization and supporting underserved populations in overcoming the obstacles encountered, could be an intervention to facilitate healthcare utilization by underserved populations. This study aimed to identify health mediation mechanisms that could influence healthcare utilization by underserved populations.</p> Methods <p>We conducted a theory-driven qualitative study from November 2021 to March 2022 with people living in settlements in France’s Southwest (Gironde) and South (Marseille). Using purposive sampling, 18 face to face interviews were conducted with underserved persons by a trained interviewer to collect data on their perceived health needs, mechanisms that could influence their healthcare utilization, and strategies they already implemented to utilize healthcare. To build the coding table, we identified psycho-social theories explaining behavioral change in healthcare utilization: one at the individual level: the Theory of Planned Behavior, and another one for the collective level: the Behavior Model for Vulnerable Populations. A thematic content analysis was performed using N vivo software.</p> Results <p>The results highlighted and confirmed five health mediation mechanisms influencing healthcare utilization by underserved populations. Perceiving no health needs and the presence of obstacles to healthcare utilization both appeared to limit utilization, while trust in a resource person and one’s individual capabilities seemed to foster healthcare utilization to reduce perceived physical discomfort. Finally, collective capabilities also appeared to foster healthcare utilization to improve physical and mental well-being.</p> Discussion <p>Health mediation would be an intervention that should help people’s perceived health needs emerge, develop trust in a resource person, and facilitate collective empowerment through an alliance between health mediators, underserved persons, and other stakeholders to compensate for/balance the structural causes of a lack of adequate care and prevention.</p>