Introduction <p>Obesity is associated with poor mental health. However, the nature and direction of this association are not well understood. This study is the first to qualitatively examine the nature of the relationship between obesity and mental health from the perspective of people living with obesity.</p> Methods <p>A qualitatively-driven multimethod research design was implemented, integrating hermeneutic phenomenological conversational interviews and focus group methods. Data from these interviews were transcribed verbatim and analysed using thematic analysis.</p> Results <p>Four major themes emerged related to: (1) Mental health difficulties and obesity: Chicken or egg?, (2) Obesity as “a literal not fitting in”, (3) Obesity as a response to trauma, (4) The importance of mental health support in obesity treatment. People living with obesity struggled to determine the direction of the relationship between obesity and mental health, but identified the mental health impact of “not fitting in” and obesity as a response to, or repellent against, childhood abuse or trauma.</p> Conclusion <p>Our findings offer a qualitative insight into the bidirectional nature of the relationship between obesity and mental health from the perspective of people living with obesity.</p>