The purpose of this case report was to demonstrate how CrossFit (CF) as a workplace health intervention (WHI) led to long-term lifestyle changes and health improvements in an inactive, sedentary individual. Therefore, we analysed the case of a 41-year-old obese man (BMI: 41.3 kg/m2) with elevated blood pressure and poor fitness. To evaluate the factors that facilitated his behavioural change, we collected quantitative and qualitative data (from 2015 to 2022) and analysed it based on the COM-B framework. Given the already great training opportunities at his workplace, we assumed that improvements in capability and motivation led to behavioural change and maintenance. Essential for this behavioural change was the fact that CF combined health-promoting training with intrinsically motivating aspects which are typical for classic sports such as challenge, a feeling of competence, and social interaction. In conjunction with rapid fitness improvements (capability), a positive feedback cycle between capability, motivation, and behaviour developed which enabled physical activity to become habitual. As a result, blood pressure was normalized, BMI (32.9 kg/m2) and resting heart rate decreased (−20 bpm), and mobility (FMS score: +89%), strength (+14 to 71%), and well-being (WHO-5 score: +12%) increased. In conclusion, CF should be considered an effective, efficient, and safe WHI with great potential for behavioural changes and maintenance.