Background <p>Patient and public involvement and engagement (PPIE) is central to research addressing health inequalities and requires involvement that reflects the lived realities of those most affected. However, PPIE often relies on a narrow group of contributors, limiting socio-economic representation and raising concerns about its relevance for inequalities-focused research. To address this, a layered PPIE strategy was developed to increase the breadth and depth of involvement, and this paper presents a case study demonstrating its use in the RETURN dental study.</p> Methods <p>A layered PPIE strategy was embedded within the RETURN study, comprising a lay researcher, a patient reference group of experienced PPIE contributors, a community advisory group representative of RETURN participants, and grassroots engagement activities designed to increase breadth and inclusivity by reaching individuals less likely to engage through formal PPIE routes. Each layer involved different types of activity and temporal arrangements, ranging from one-off engagement to sustained, longitudinal relationships. In total, over 300 PPIE collaborators contributed to the development of the RETURN study, including co-production of the intervention and patient-facing materials, refinement of patient information sheets and questionnaires, input into recruitment practices, and dissemination activities.</p> Results <p>Each PPIE layer contributed distinct forms of input, with differing contributions, challenges, and lessons learned. Quotations and concrete examples from the RETURN study illustrate the impact of involvement across layers. Differences in perspectives across layers provided valuable insights and, taken together, enabled a more meaningful and inclusive form of PPIE than would have been achievable through a single layer alone.</p> Conclusions <p>The layered PPIE strategy presented in this paper can strengthen inclusivity within health inequalities research by combining multiple forms of involvement aligned to different purposes and stages of the research. Engaging both experienced PPIE contributors and people less likely to be involved through conventional routes enabled perspectives from across the socio-economic spectrum, while preserving depth and rigour. Layered approaches offer a practical way to move beyond tokenism and support meaningful, context-sensitive involvement in complex research programmes.</p> Trial registration <p>ISRCTN (<a href="http://www.isrctn.org/">http://www.isrctn.org/</a>) 84666712, 12.01.2021</p>