This systematic review aims to synthesize the active ingredients, and identify a list of promising behaviour change techniques (BCTs), likely to be present within physical activity and / or dietary interventions in achieving weight loss in overweight and obese healthcare staff. Four electronic databases were searched in February 2021: PsychINFO, CINAHL, PubMed and MEDLINE (no start date-2021). Studies were eligible for inclusion if they: (1) described a quasi-experimental or cluster, cohort or randomised control trial; (2) implemented workplace-based physical activity and / or dietary interventions versus a less intensive intervention or usual care; (3) targeted predominantly (> 50% of participants) overweight or obese healthcare professionals; and (4) reported a weight loss related outcome and included data on that outcome at least 3 months after the intervention began. Three reviewers used the Behaviour Change Technique Taxonomy v1 to extract BCTs with the aim of identifying a list of “promising” BCTs, which were those that were present in interventions that reported a statistically significant difference in weight loss. Nine studies were included in the review. The majority (n = 7) reported a significant reduction in weight post-intervention. A combined physical activity and dietary intervention (n = 8) was the most common type of intervention. Twenty-five BCTs were identified as “promising”. Instruction on how to perform the behaviour (n = 9), behaviour practice/rehearsal (n = 8) and self-monitoring of behaviour (n = 6) were the most promising BCTs. The contents of behaviour change interventions are complex and rely on accurate reporting of intervention components and BCTs to allow concrete and robust assumptions to be made regarding which factors are most effective at achieving a desired outcome. Fundamentally the lack of research exploring the effectiveness of physical activity and dietary interventions on weight loss in overweight and obese healthcare staff and the poor quality of existing research, warrant more investigation.