BACKGROUND: Overweight and obesity are major public health problems and an increasing global challenge. In lieu of wider policy changes to tackle the obesogenic environment in which we presently reside, improving the design of individual-level weight loss interventions is important. AIM: To identify which aspects of the Camden Weight Loss randomized controlled trial weight loss intervention participants engaged with, with the aim of improving the design of future studies and maximizing retention. METHOD: A qualitative study comprising semistructured interviews ( n = 18) and a focus group ( n = 5) with intervention participants. RESULTS: Two important aspects of participant engagement with the intervention consistently emerged from interviews and focus group: the advisor-participant relationship and the program structure. Some materials used during the program sessions were important in supporting the intervention; however, others were not well received by participants. CONCLUSION: An individual-level weight loss intervention should be acceptable from the patient perspective in order to ensure participants are engaged with the program for as long as possible to maximize favorable results. Providing ongoing support in a long-term program with a trained empathetic advisor may be effective at engaging with people trying to lose weight in a weight loss intervention.