Unhealthy eating and physical activity behaviours are common among nurses. As nurses spend a substantial proportion of their waking hours at work, interest in delivering interventions in the workplace to improve this populations' eating and physical activity behaviours is growing. This programme of research aimed to systematically develop evidence-based and theory-informed recommendations for a workplace intervention to change nurses' eating and physical activity behaviours. Methods: A systematic literature review of published randomised controlled trials was undertaken. Factors that behavioural theories suggest may influence nurses' eating and physical activity behaviours were identified through theoretical domains framework-informed qualitative interviews and a survey of nurses. Intervention recommendations were specified in terms of (i) intervention functions and policy categories using a Behaviour Change Wheel and (ii) theory-informed behaviour change techniques using a behaviour change technique taxonomy. Evidence related to the parameters of effectiveness for each technique was also taken into account during this intervention specification process. The selected techniques were then combined into a conceptual overview of a potential workplace intervention. Results: Data from 13 randomised controlled trials indicate workplace-based behaviour change interventions targeted to this population are effective in decreasing body weight. The evidence base is, however, limited in quantity and quality. Nurses' beliefs about important determinants of eating and physical activity behaviour change were identifed across 16 qualitative interviews and 245 survey responses and key determinants included: environmental context and resources; behavioural regulation; emotion; beliefs about consequences; knowledge and optimism. Based on this behavioural diagnosis, 24 behaviour change techniques suitable for targeting the identified determinants were chosen and combined into a potential workplace intervention. Conclusions: This thesis illustrates the utility of the Theoretical Domains Framework, the Behaviour Change Wheel and the behaviour change technique taxonomy for developing workplace intervention recommendations. The proposed recommendations address a gap in the current evidence base. Such an intervention, if implemented, has the potential to improve nurses' eating and physical activity behaviours and in turn, the health of nurses and the quality of healthcare delivery.