Background: Loneliness is a highly prevalent, harmful, and aversive experience which is fundamentally subjective: social isolation alone cannot account for loneliness, and people can experience loneliness even with ample social connections. A number of studies have qualitatively explored experiences of loneliness; however, the research lacks a comprehensive overview of these experiences. We present a protocol for a study that will, for the first time, systematically review and synthesise the qualitative literature on experiences of loneliness in people of all ages from the general, non-clinical population. The aim is to offer a fine-grained look at experiences of loneliness across the lifespan. Methods: We will search multiple electronic databases from their inception onwards: PsycINFO, MEDLINE, Scopus, Child Development & Adolescent Studies, Sociological Abstracts, International Bibliography of the Social Sciences, CINAHL, and the Education Resource Information Center. Sources of grey literature will also be searched. We will include empirical studies published in English including any qualitative study design (e.g. interview, focus group). Studies should focus on individuals from non-clinical populations of any age who describe experiences of loneliness. All citations, abstracts, and full-text articles will be screened by one author with a second author ensuring consistency regarding inclusion. Potential conflicts will be resolved through discussion. Thematic synthesis will be used to synthesise this literature, and study quality will be assessed using the Joanna Briggs Institute Critical Appraisal Checklist for Qualitative Research. The planned review will be reported according to the Enhancing Transparency in Reporting the Synthesis of Qualitative Research (ENTREQ) statement Discussion: The growing body of research on loneliness predictors, outcomes, and interventions must be grounded in an understanding of the lived experience of loneliness. This systematic review and thematic synthesis will clarify how loneliness is subjectively experienced across the lifespan in the general population. This will allow for a more holistic understanding of the lived experience of loneliness which can inform clinicians, researchers, and policymakers working in this important area.