Abstract Background National Health Service (NHS) staff support service users to change health-related behaviours such as smoking, alcohol consumption, diet and physical activity. It can be challenging to discuss behaviour changes with service users hence training is needed to equip staff with up-to-date, evidence-based behaviour change skills. In order to identify how training may help to improve health professional skills in this area, this study evaluated change in professionals’ behavioural determinants following an online behaviour change skills module as part of Making Every Contact Count (MECC) training. Methods This evaluation comprised a within-subject design in which staff from one Northwest England NHS Trust completed a 9-item survey immediately before and after training. This prospective survey identified behavioural determinants regarding adhering to MECC recommendations to hold health conversations with service users and provided written comments about their training experiences. Individuals working within the Trust in clinical or non-clinical roles were eligible to take part and were invited to contribute to the evaluation upon uptake of their usual NHS staff online training programmes. Results Of participants completing the evaluation (n=206), 12 professional cadres accessed the module, most being female (91%), nurses/midwives (43%), working in children and family services (48%), aged 22 - 62 years. Eight behavioural determinants increased significantly following training, with effect sizes ranging from sizes ranging from 0.27 to 0.51; ‘identity’ did not change. Content analysis of written feedback (n=256) indicates that training enhanced staff behaviour change skills, modelled a productive and specific method of adopting a patient-led approach to behaviour change conversations, and identified that staff may require further support with embedding skills in practice. Conclusions Behaviour change science can be translated into useful learning for NHS staff. Online training can engage staff in learning about behaviour change skills and increase their behavioural determinants to adopt these skills in practice.