Objective: The objective of this review was to identify, appraise, and synthesize the best available evidence related to participation in outdoor nature-based therapeutic recreation programs for adults with a mental illness living in the community. Introduction: Therapeutic recreation is posited to be beneficial for persons living with a mental illness. Research evidence indicates that therapeutic recreation programs can foster mental health recovery. It is important to understand the effectiveness of this from the perspective of persons living with mental illness how outdoor nature- based therapeutic recreation programs are meaningful and helpful for recovery. Inclusion criteria: This review considered studies that collected qualitative data on the experiences and perspectives of adults with a mental illness regarding their participation in outdoor nature-based therapeutic recreation programs. Methods: The databases PsycINFO, CINAHL, MEDLINE, Scopus, and Informit, as well as unpublished sources in gray literature (Google Scholar, OpenGrey), were searched and reference lists were checked to locate any additional studies. Studies published in English were considered, with a date range from inception to 2019. Three reviewers independently assessed the methodological quality of the studies that met the inclusion criteria using the JBI critical appraisal approach for qualitative research. Data were extracted by one reviewer using the standardized qualitative extraction tool and checked for accuracy by three other reviewers. The qualitative research findings were pooled using JBI methodology. The JBI process of meta-aggregation was used to identify categories and synthesized findings, and a level of confidence was assigned to both synthesized findings. Results: Eighteen papers met the inclusion criteria and were included in the data extraction phase. A total of 84 findings were extracted and aggregated into six categories based on similarity of meaning and two synthesized findings. The methodological quality of the studies varied, and the overall level of confidence of the synthesized findings was determined to be moderate. Conclusions: This review identified that persons living with mental illness perceive outdoor nature-based therapeutic recreation as enjoyable and that therapeutic recreation makes a positive contribution to mental health. Congruent with the literature, therapeutic recreation offers a socially inclusive and psychologically safe environment. The intentionally structured social milieu enhances the formation of social relationships and meaningful connections for persons with mental illness. Elements linked with psychological well-being, such as intrinsic motivation, overcoming perceived challenges, and finding purpose and meaning, are enhanced through participation in therapeutic recreation in outdoor nature-based settings. Increased levels of physical activity, greater self-esteem, and enhanced sense of identity were some of the perceived positive changes. This review provides important insights into the subjective needs of persons with mental illness who undertake therapeutic recreation in outdoor nature- based settings. The qualitative findings can inform health care providers, or those interested in therapeutic recreation programming, to use alongside quantitative evidence of effectiveness to design nature-based therapeutic recreation activities that are meaningful for persons with mental illness. Limitations of the research were that papers published in languages other than English were not searched, and papers not located may have influenced the findings of this review.