Abstract Background Critical incident debriefs are a commonly used occupational health tool for supporting staff after traumatic work incidents. However, there is a dearth of literature evaluating training programmes for debrief facilitators. Aims To evaluate a 5-day training programme to equip healthcare, social care and voluntary, community and social enterprise sector staff to act as post-incident peer supporters and debrief facilitators. Methods A mixed-methods, single-arm, before-and-after study. Data were collected at baseline and post-training. The quantitative outcome measure was ‘Confidence’; the sum of two items measuring confidence in (i) supporting peers after critical incidents and (ii) facilitating post-incident structured team discussions. At post-training, quantitative and qualitative feedback regarding experiences and perceptions of the training was also gathered. Results We recruited 45 participants between October 2021 and January 2022. Confidence in supporting peers following incidents and facilitating post-incident structured team discussions increased significantly following the training, t(35) = −6.77, P < 0.001. A majority of participants reported they would do things differently because of the training and that they found the training relevant, useful and engaging. Summative content analysis of qualitative feedback indicated that participants (i) believed the role plays were an important learning tool and (ii) thought it was important that the trainer was engaging. Some participants would have preferred in-person delivery. Conclusions Participants valued training in post-incident peer support and debriefing skills. Organizations implementing post-incident support pathways could usefully include this training and ensure optimal uptake and engagement by (i) providing in-person and online delivery options and (ii) including role play as a learning technique.