Long-distance walking is an ancient activity practiced across cultures for many reasons, including the improvement of one's health. It has even been suggested that long-distance walking may be considered a form of psychotherapy. This scoping review examined the relationship between long-distance walking and mental health among adults. Publication trends and definitions were also examined, and the reason why long-distance walking may have therapeutic effects was discussed. Systematic searches in three online databases were performed using a selection of long-distance walking terms. Both quantitative and qualitative studies were included if they examined associations between long-distance walking and mental health in an adult population. Mental health was conceptualized in broad terms, including descriptions of mental states as well as more specific measurements or notions of mental health. A total of 8557 records were screened and 26 studies were included, out of which 15 were quantitative, 9 were qualitative, and 2 were mixed. The findings showed that long-distance walking was positively related to mental health. This was most consistent with regard to emotional distress compared to somewhat inconsistent findings regarding well-being. Therefore, long-distance walking may be more appropriately used to counter some personal or emotional struggle rather than to achieve hedonic pleasure.